All magic items (in the core rules) are imbued with power on creation. I like the idea of magic items that draw power from their users to activate their effects. This article describes a way to handle this — User-Provided Mana (UPM) items.
User-Provided Mana Items in Play
UPM items are pretty straightforward. You activate one by giving it spell power (spell slot or magic points) and meeting any other requirements it has (such as uttering a command word or paying experience points) and the effect happens.
Because the power is drawn entirely from the user, the degree of effect is based on the caster level of the user. A scroll of fireball has range and damage as if cast by the user, rather than by the creator of the scroll.
Cost of User-Provided Mana Items
The simplest model I’ve found for UPM items that I think will work is to remove the caster level component from the market price of the item. A UPM scroll will cost 25 gp per level of the spell on the scroll, a UPM potion will cost 50 gp per level of the spell of the potion, and so on.
This looks frighteningly low, in some ways. It costs only 300 gp for a UPM use-activated single-use item (such as a potion or consumable wondrous item) of a sixth-level spell.
However, this still requires the user to use a sixth-level spell slot — one that he could otherwise have used to cast a spell that he knows or has prepared. This 300 gp is not for the sixth-level effect, but for the ability to use a 6th-level spell slot on a spell the caster does not have prepared or does not know (and in this case, in fact, he need not even be capable of learning the spell).
The only place I’m concerned is with permanent, at will items. A UPM rod that gives the ability to cast a spell at will (that you don’t know!) would cost 2,000 gp per spell level. This doesn’t bother me much with most classes, but it gives a potentially huge benefit to sorcerers, for the cost.
Creating User-Provided Mana Items
To create a UPM item, you must have the Create User-Provided Mana Item feat. It allows you to create magic items that draw on their users rather than on you, when you create the item.
Create User-Provided Mana Item [Item Creation]
You can create magic items that draw their power from their users
Benefit You may choose, when you create a magic item, to have it draw its power from its user. Normal enchantment rules otherwise apply, but remove the ‘caster level’ component from the market price of the item.
For example, a potion of arcane sight normally has a market price of 750 gp. A UPM potion of arcane sight has a market price of only 150 gp.
Special Other feats that modify item creation (such as Rapid Scribing) may still apply. This feat modifies the use of any and all Item Creation feats.