Custom Magic Items

[Naez]

I'm looking for the rules to create magic items that mimic spells to help out a couple of my party members. From the rules in the SRD a custom continuous Mage Armor item would cost 2000 gp. That seems a bit low and I feel like there's a factor that I'm missing. Can anyone point me to more detailed rules?

[torrasque666]

Its because its 1(spell level)*1(caster level)*2000(continuous, doesn't fall into one of the price modifying categories)

[SinsI]

Wrong. In this case it is covered by "similar item" - so you are looking at Bracers of Armor, with the cost of Bonus squared × 1,000 gp.

[Segev]

You only use the "spell effect" calculation rules as a last resort. Most of the "gives a +X bonus" type items use formulae spelled out specifically for that kind of bonus to that particular stat.

Look at Bracers of Armor for what "mage armor" as a magic item does.

(Wands and Scrolls and Staves use spells directly, but that's because they literally store castings of spells to be expended later.)

[SinsI]

That being said, if you have a Wizard in your party that prepares Mage Armor anyways you can buy a few Pearls of Power 1 and get almost the same result for 1-3k gp.

[Naez]

Mage armor was only one of the effects I was wondering about but there's others as well such as an item of at-will Swift Invisibility (1st level Bard spell), and continuous Shield which while similar to mage armor but has additional effect as well that would not be covered by braces of armor.

[Surpriser]

In that case: There are no rules, only guidelines.

The only thing you can do is to compare with existing items and then set a price is in line with the abilities you want. This is different for each individual item and cannot be answered in general.

For your given examples:
At-will Swift Invisibility: Same price, maybe slightly lower than Ring of Invisibility (20k), unless it does not need a body slot (then *1.5). The lower duration of the spell is partly offset by the fact that you can disappear at a moments notice.

Shield: The baseline is again the Bracers of Armor +4 (16k). The differences are: Different bonus type (natural/deflection cost double) and the defense against Magic Missile and incorporeal touch attacks. I would probably set the final price at 32k, same as a ring of protection.

[Felyndiira]

Keep in mind, also, that the magic item creation guidelines are just a guideline. Even though there's no items like it, a GM is perfectly within his rights to rule that a continuous item of Arrow Mind would cost more than just 1000 GP.