Magic Item which gives extra spell slots

[Shin Okada]

As a DM, I am planning to create a new item which gives some extra spell slots to the user. Possibly, it is a ring or some other item which occupies a body slot and works only for arcane casters or just for wizard.

Instead of doubling the number of spell slots of certain spell level, the item will just give the user bonus spell slot, say one extra, for a certain spell level. I mean, an item which gives one each of additional spell slots for 1st-5th spell level, assuming the user can cast spells of that level.

I know many people compares Pearl of Power, Memento Magica (Magic Item Compendium) and Ring of Wizardry and says Ring of Wizardry is rather too expensive. If so, how much should be the "reasonable" cost for such an Item?

 

[Celebrim]

I consider additional spell slots to be a quite potent ability, though it's more potent for a caster that has to prepare spells than for one with spontaneous spells.

I'd price your item at not less than 48,000 g.p. Five additional spell slots is rather nice.

I should say that I tend to be rather generous regarding these sorts of things because I rather like items with broad utility compared to items that do one thing really well. I can easily imagine more conservative DMs pricing that as high as 73,000 g.p.

 

[thompsja]

Price for a extra spell is the square of the spell level X 1000. An extra 1st level spell is 1,000, an extra 6th is 36,000. Your example of one extra of the first five is ( 1 + 4 + 9 + 16 + 25 ) * 1000 = 55,000 gp.

 

[Nagol]

For an unslotted example, consider the Pearl of Power in the DMG/SRD. Though the price reduction back down to base cost is probably due to the extra limits (can only recover a spells previously cast as opposed to the ability to prepare an additional spell upfront and taking a round for the recovery).

Compared to the pearl the ring is overpriced at the low end even if you assume the purchaser is going to make full use of its abilities (i.e. gains ~8 1st level spells at the cost of a 20,000 gp vs. 8x1,000 gp and that's not taking into account multiple similar abilities ) and almost fair prices at the higher versions (~5 4th level spells at the cost of 100,000 gp vs. 5x16.000 gp).