This DM wouldn't allow into the campaign that magic tea-ball as proposed…
If a PC pitched this original magic item to a magic craftsman in my campaign or if the player of a magic craftsman PC in my campaign pitched this item to me, I'd want to know the item's precise mechanics before determining its price. I'm speculating, but the question makes the proposed original magic item sounds like this:
Tea-ball of Toxins I: A creature holding this item can take a full round action that provokes attacks of opportunity either to load it with a dose of noninhaled poison that the bearer also has in hand or to unload its contents. When it's loaded, the bearer can take a standard action to utter a command word and pick a creature within 30 ft. The item then teleports from the bearer's hand into the creature's stomach where the item delivers its contents, expending the dose of poison. (The item doesn't teleport if the DM rules that the picked creature doesn't possess a stomach.) The owner can take a standard action to utter a different command word to cause the item to teleport from the creature's stomach back into one of the owner's empty hands. (The item remains in the creature's stomach if its owner's hands are full.)
This DM wouldn't allow this item as its described above into his campaigns. Most binary combat effects in D&D 3.5 have at least one point of failure—that is, no matter how long an attacker takes to activate an ability, that ability may still not affect the defender, usually because the attacker failed a roll (like an attack roll) or because the defender succeeded on a roll (like a saving throw). One such effect is delivering a poison. (Typically, delivery fails due to a failed attack roll.) The tea-ball of toxins I bypasses the normal possibility of failure that comes with delivering a poison and, instead, delivers a poison automatically. For this DM, that's simply a nonstarter.
See, in a typical campaign, a poisonmaker can pretty much create any poison (assuming appropriate abilities, gp, skill, time, raw materials, and other individual factors)—the poisonmaker need not discover during its career a poison's recipe, for instance. This means if there's a poison somewhere in the game that has consequence solely upon delivery, the game may be broken, and the possibility of a broken game doubles if a poison can be modified by other game elements so that it has consequences automatically upon delivery.
I've been playing this game for a while, and I don't know every poison, and I certainly don't know if any combination of abilities can modify a poison so that it has consequences upon delivery. I honestly wouldn't expect any DM to have that information handy, and, given the game's vastness, I suspect that even a DM that thought she had all that information will have players that find loopholes and overlooked gems.
Still, if the tea-ball of toxins I is allowed into an existing campaign anyway, the setting may have to be retconned to account for it. That is, unless the tea-ball of toxins I is tightly controlled (through culture, economics, magic, religion, or some other means; also see here), potentially anybody can take a standard action to poison anyone that's within 30 ft. and that has a stomach, and this requires no special skill on the part of the poisoner. A setting with zero controls on the tea-ball of toxins I is likely to look less like a typical high fantasy setting and more like a Wild West setting. (By the way, budding author, you have at least one customer for your high fantasy Wild West setting High
Noon Tea—in fact, I'll take two if it's not predicated on magic rocks.)
Really, no matter how much time the tea-ball of toxins I takes to use a second time, if using it at all could—possibly with enough research—automatically overcome such a wide variety of challenges, I couldn't allow the item into a typical existing campaign.
Special: That magic item's relationship to that campaign
In the campaign in question, the DM had the player describe some poisons the PC could make. It's unclear if these poisons are in addition to the normal poisons every poisonmaker can make or if these are the only poisons that poisonmaking PC can make. If the latter, this reader suspects the DM is keeping a short leash on poisonmaking by limiting the availability of poison recipes… for some reason. That's a fine house rule (a term I don't use pejoratively), but it means that only the DM can set a price on this item: Only the DM knows if the magic item should have a low price because it's a pretty much a toy (i.e. the PCs will never discover the recipes of significant poisons so delivering them automatically will only ever be a minor debuff) or if the magic item should be at least a minor artifact therefore beyond price (i.e. the PCs will discover the recipe for an initial-damage-a-god-dies and secondary-damage-the-god's-plane-is destroyed poison—and could I take a look at that recipe, please?).
…But this DM would allow a similar magic item…
In short, this DM would say, "Either the victim gets a saving throw against the tea-ball or the tea-ball's user makes a ranged touch attack against the victim. Trust me: You don't want me to allow the tea-ball to appear automatically inside the victim and deliver its poison—because that victim could totally be you." Then I'd offer a counter-proposal like this:
Tea-ball of Toxins II: A creature holding this item can take a full round action that provokes attacks of opportunity either to load it with a dose of noninhaled poison that the bearer also has in hand or to unload its contents. When it's loaded, the bearer can take a standard action to utter a command word and pick a creature within 30 ft. The picked creature makes a saving throw (Will DC 16). If the creature succeeds, the item remains in the bearer's hand. If the creature fails, the item teleports from the bearer's hand into the creature's stomach where the item delivers its contents, expending the dose of poison. (The item doesn't teleport if the DM rules that the picked creature doesn't possess a stomach.) The owner can take a standard action to utter a different command word that causes the item teleport from the creature's stomach back to one of the owner's empty hands. (The item remains in the creature's stomach if its owner's hands are full.)
Faint conjuration; CL 7th; Craft Wondrous Item, dimension door; Price 2,400 gp.
Why 2,400 gp? Not because of Table 7–33: Estimating Magic Item Gold Piece Values (Dungeon Master's Guide 285), but instead because that's about the price of the typical magic weapon that possesses a +1 magic enhancement bonus (see here).
This DM is comparing the tea-ball of toxins II to other similar items, and a +1 poison ring is similar because of how the action economy works. See, a poisoner holding a loaded tea-ball of toxins II on his turn has a choice either to take a standard action to use it or to make an attack with a poison ring (Dragon Compendium Volume 1 111, 115) (45 gp; 0 lbs.).1 For the poisoner to administer her poison using the tea-ball of toxins II the victim must fail a Will save and to administer her poison using a poison ring the poisoner must succeed on a melee touch attack against the victim. Those are—at least at low levels—approximately equivalent.
Thus, when a poisoner is looking for a magic weapon, she'll typically consider a +1 poison ring that has a price of 2,345 gp—and with which, at the levels its first available, the poisoner will be making one attack per turn. So a tea-ball of toxins II with its price of 2,400 gp is an attractive alternative: The poisoner can pay either to do better what she can already do or for a brand new option.
…Or even a similar, less pricey (largely) one-use magic item
Finally, because I'm a little fussy, I might offer a counter-counter-proposal in the following item:
Tea-ball of Toxins III: A creature holding this item can take a full round action that provokes attacks of opportunity either to load it with a dose of noninhaled poison that the bearer also has in hand or to unload its contents. When it's loaded, the bearer can take a standard action to utter a command word and pick a creature within 30 ft. The picked creature makes a saving throw (Will DC 14). If the creature succeeds, the item remains in the bearer's hand. If the creature fails, the item teleports from the bearer's hand into the creature's stomach where the item delivers its contents, expending the dose of poison. (The item doesn't teleport if the DM rules that the creature doesn't possess a stomach.)
Faint conjuration; CL 5th; Craft Wondrous Item, blink; Price 250 gp.
…Because nobody but an adventurer wants back a tea-ball that's been in a dude's stomach—yuck!—, yet no true adventurer passes up 250 gp just because she must slit a defeated foe's belly and root around in it to get it! Still, being unable to recover conveniently the item will make the item, in many cases, simply irrecoverable (Maybe it can still be recovered, but just, y'know, like, later?) With this in mind plus its reduced saving throw DC, decreasing the price of a tea-ball of toxins III to about 10% of the price of a tea-ball of toxins II seems to this DM a reasonable adjustment. (The extra 10 gp is make the item's price more convenient.) This item, too, may still influence the setting: In a campaign that features frequent poisonings, a guy could make serious dough selling laxatives.
Note: The saving throw DCs for tea-balls II and III were computed using the minimum Intelligence score a wizard needs to cast the spell that is the prerequisite for each item's creation. The item's caster level is likewise based on that imaginary wizard's minimum caster level to cast that prerequisite spell. Another DM could raise or lower those DCs and caster levels as suits the campaign. Further, this DM thought that a (mostly) disposable magic item's saving throw DC and caster level should be lower than a permanent magic item's; another DM may have a different opinion. Also, this writer has blithely ignored the physiological ramifications of dozens of guards each armed with a tea-ball of toxins who collaborate to pop an intruder by overfilling its stomach with magic tea-balls. An individual DM must deal with that issue himself, perhaps by limiting even a normal creature's stomach capacity and having items that would cause that capacity to be exceeded just fail to operate.
1 For those unfamiliar with the awesome sauce that is a poison ring, it's a totally a mundane light simple weapon that can be loaded with one dose of injury poison. The wearer can make with the ring a melee touch attack that, if successful, deals the target 1 point of damage (2 points on a critical hit) and delivers the poison. (It doesn't need to be loaded for a wielder to deal with it its normal, nonpoison damage.) A character won't have a poison ring if the DM banned the ring from the campaign, the DM allows anyone to make touch attacks (see here), or the creature lacks fingers, but if none of those apply then an adventurer really should have one or two or ten. By the way, the game puts no limit on the number of mundane rings a typical creature can wear, so—um—beware folks wearing rings, I guess?