We use the following rules for magic items granting feats. Note that some feats of course are better than others, so these rules are just guidelines:

Enchantments that Mimic Feats

You must have the feat in your sheet (and not added from a magic item) in order to apply a it to a magic item.

Use the following formula to determin the price of adding the power of a feat to a magic item: (Number of prerequisites +1) squared, x 1000 gp.

Eg: Spell penetration has no prerequisites ((0 + 1) x 1 x 1000 = 1000 gp). Greater weapon focus has three prerequisites (proficiency with selected weapon, Weapon Focus with selected weapon, fighter level 8th. (3 + 1) x 4 x 1000 = 16000 gp)

Epic feats use the same formula, multiplying the result by x10, and adding a further 200,000gp.