I believe it was a sidebar in the Arms and Equipment Guide.
Memory serving it was 10k for a feat, with an additional 10k per prerequisite feat.
So, ignoring slot affinity for this example, a bracelet that granted the wearer access to the Power Attack feat would cost 10k, whereas a headband that granted access to the Whirlwind Attack feat would cost 50k. 10k for the feat, and an additional 40k for the Dodge, Mobility, Spring Attack, and Combat Expertise requirements. Important to note that the wearer would not have access to the prereq feats unless they were included seperatly (which would end up costing a pretty penny).
If a feat grants a particular bonus similar to those listed on the DMG chart, use those guidelines instead. A Ring of Skill Focus, say, should be priced as an item that grants a +3 bonus to a skill, rather than an item that grants a feat.