Of all the character abilities in the game, feats are the only ones that cannot be reliably reproduced with magic items. Feat slots are rare and valuable, almost overpriced due to their strictly limited supply. If magic items can replicate high ability scores, attack bonuses, skills, and even some class abilities, what’s the gold piece price to assign to a feat?
Sean K Reynolds estimates a feat is worth roughly 25,000 gp. A sword that grants the wielder Combat Reflexes might cost this much. However, he also admits that feats can have radically different values, which one could argue ought to bear true in magic item pricing; Alertness (+2 to two skills) is only worth 1,000 gp by the chart, whereas Spell Focus is worth something perhaps more substantial.
Interestingly, a lot of feats do weigh in at around 1,000 to 1,200 gp. The three “+2 to one save” feats equate to a 4,000gp magic item, the Cloak of Resistance +2, for 1,333 gp per feat. Both Dodge and Improved Natural Armor grant +1 to AC, worth roughly 1,000 gp, although Dodge is more limited in its use. Point Blank Shot and Weapon Focus offer +1 to hit, equal to half a +1 weapon. So far feats look quite weak, kept artificially rare as a matter of game balance.
On another scale, consider what a feat slot might be worth if the player can choose any feat he likes, comparing the human to other races. An elf has bonuses and penalties which we may consider to cancel out, immunity to one spell and +2 to one seventh of spells, further vision, some free weapon proficiencies, a +2 bonus to three skills and their secret door ability. We might consider that these abilities together are worth one feat and one skill point per level. +2 to saves (4,000 gp) applicable to only one school of magic, which will be less than half of saves, we might price at 400 gp including the Sleep immunity. Low-light vision and weapon proficiencies are hard to benchmark, but the skills are easily calculateable at three sets of 400 gp. Our human has one feat and one skill point, worth 100 gp per level. Suppose we average that skill point to 1,000 gp and the feat to 1,200 gp, are martial weapon proficiencies on a non-combat character, low-light vision and the secret doors trick worth 1,400 gp? Perhaps.
Lets try another race, the halfling. His ability score modifiers could be said to balance out. He has small size and slower speed, which we may likewise consider to be a set of fair trades. +2 bonus to four skills is 1,600 gp. +1 to saves is 1,000 gp (Cloak of Resistance). +2 on saves vs fear, if we imagine fear is one third of all Will saves this is worth around 450 gp. +1 attack/damage with thrown weapons is worth a good 2,000 gp (magic weapon). In all, we might price the halfling as much as 5,050 gp, giving our human’s feat slot a value of around 3,800 to 4,000 gp.
Naturally, feats are worth a lot due to the limits placed on them, which is a feature of game just like magic item slot limits. In that regard, it’s probably best that most feats can’t be duplicated by magic items, especially since some are so cheap in terms of equivalent gold value.