There are two answers to this question.
The really horrible answer is: jewelry takes as long to make as its value according to the bog standard craft rules. Don't try to think about the economics of it and certainly don't try to make a living at it.
The not so horrible answer is: house rules. I recommend the new crafting rules from the sourcebook by Frank and K called "Book of Gears." as a basis. They ... articulate most of the things that are broken. Unfortunately there are no good rules presented.
Quoth the sourcebook:
An overhaul to the Craft rules may sound fairly unbalancing, as the current Craft rules were created to prevent characters from making a lot of money and potentially destabilizing their games with an influx of magic items. Unfortunately, like Level Allowance, the heavy nerfing to Crafting resulted in a lot of characters simply becoming unviable, a lot of very dumb things happening all around, and it still doesn't actually stop characters from breaking the game if they really want to. If the party is made out of Elves, they can simply set a single skill rank on fire and announce that they're going to spend 100 years farming, making trained Profession (Farmer) checks every week. That'll get them about 6 gp a week for the next 5,200 weeks -- for a total of 31,200 gp at first level before they even start adventuring. And as elves, they can honestly just spend 200 years farming or spend some real skill ranks on that to get even more money.
It identifies the sacred cows of the crafting rules... and the pdf I found seems to have some suggestions as to new rules.
Jewelry is worth whatever someone is prepared to pay for it. Generally this works to an offer to not give you steel poisoning. (Acute slices to the liver can cause quite remarkable allergic reactions). Generally speaking, it should be worth enough to pay for the cost of crafting it, the cost of maintaining the shop, the cost of the raw materials, and the amortized cost of the education and apprenticeship (and all the materials that went into that) that went into leanring how to craft it.
Here's a reference on jewelry.
My personal recommendation would be to blatantly steal the crafting rules from Ars Magica City & Guild. While it's a completely different system, it's pretty mappable in terms of skill ranks. (Every 4 ranks in a skill should be 1 point in ars magica, give or take.) And it provides acceptable rules for how to make a living from it. It you care about making art then take a look at the artists section of Art & Academe (Also an ars magica suppliment.) Between the two of them, they will provide a far more solid foundation for crafting and craft rules than 3.5. (Though I would totally keep the 3.0 haste spell.)