From Arms and Equipment Guide:
"Pricing feats for magic items is a very fuzzy area. If a feat is purely mechanical, default to rules in the Dungeon Master's Guide with an adjustment for the fact that the bonus has no type...
Metamagic feats should adjust the level of the spells to which they apply, and thus change the price. While this is still a matter of judgement, consider increasing all the spell levels by +1 if the item effects spells of 0-3rd level, by +2 if the item affects spells of 0-6th level, and by +4 if the item affects spells of all levels.
A general guideline for other kinds of feats is that they cost +10,000 gp, plus another 5,000 to 10,000 gp per prerequisite."
Demiurge out.