How do I determine the special ability bonus of a homemade ability in Pathfinder?

Question

In the campaign I run with some of my friends, the fighter in the group asked me if it was possible to have a sword that could turn the damage he dealt into hp, very much like the vampiric touch spell. I looked into it and wasn't able to find any item that fit that description, so I told him I didn't think it was possible. However, we recently had a new person join us who decided she wanted to play as a wizard with an emphasis on magical item creation. As such, I looked into the rules regarding creating your own magical arms and armor and figured out what she would need to do. My problem is that I don't know how much it would cost to make the weapon in question. In the PRD, it gives estimated values for enchanted weapons based on the enchantment and ability bonuses, but because it's not a pre-made ability, I don't know what the bonus would be for the "vampiric" special ability.

My question is: how do I calculate the special ability bonus? Is it just the spell level, or is there some equation that is used to determine it based on other values?

Answer 1

When creating a new magic item, compare it to a similar item

In other words, how does this weapon special ability compare to existing weapon special abilities? What does it seem like it's about equal to?

In this case Pathfinder has nothing that's precisely comparable, but Pathfinder's predecessor Dungeons and Dragons 3.5 does have such a thing in the form of this weapon special ability:

• The weapon special ability wrathful healing (Enemies and Allies 20) (+3 bonus; 0 lbs.) causes a melee weapon to heal the wielder of half as many points of damage as the wielder dealt with the weapon to a creature. Healing beyond the wielder's maximum hp has no effect. A wielder that's instead damaged by positive energy is damaged by this healing. Caster Level: 15th; Prerequisites: Craft Magic Arms and Armor, regenerate.

The DM should adjust the bonus, effect, and prerequisites to fit Pathfinder and the campaign. Converting all the damage to healing should require a higher bonus, the weapon special ability greater wrathful healing probably worth, by the game's estimation, a +5 bonus, if such a weapon special ability is available at all.

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An Aside
Such a weapon isn't appropriate for all campaigns as, once the weapon's in the PCs' hands, rarely is noncombat healing an issue. For some groups, this makes the game more fun; for others, this sucks the fun right out. Consider carefully the ramifications of unlimited out-of-combat healing. Stabbing a dozen or so chickens to heal between encounters might not be what players expected when they were told this was a heroic fantasy adventure game.

Answer 2

For what it's worth there is a similar typed item, in the form of Vampiric Gloves. They allow for a 3/day use of Bleed and Vampiric Touch, as well allowing for the use of Vampiric Touch to counter a bleed effect or allowing Vampiric Touch as a ranged touch against creatures that are dying or suffering a bleed effect. They are priced at 18,000.

As per pricing rules for a fixed cost addition(treated as a Use Activated/Continuous), it would be Spell Level x Caster Level x 2000 or 3 x 5 x 2,000 for a price of 30,000.