Hmm.
In 3.0, skill items were bonus squared x 20 gp.
So the original Choker of Eloquence, in the 3.0 Arms and Equipment Guide, at 6,000 gp, was close to being right at 2,000 + 2,000 + 2,000. But it should have been 2,000 + 3,000 + 3,000 = 8,000 gp. That's in 3.0. How they came up with 24,000 in 3.5 boggles the mind. About the prerequisites, really, why do you need Craft Wondrous Item? Why not delete that and replace it with 'Special: Must have given an eloquent speech'?
OK, sorry for the sarcasm.
The Circlet of Persuasion is 4,500 gp in both 3.0 and 3.5, which seems like another cut and paste error. 3 x 3 x 500 = 4,500. Skill items in 3.5 are 5 times more expensive than in 3.0 (bonus squared x 100 vs bonus squared x 20), so if we extrapolate, the price of a Circlet of Persuasion in 3.5 would be 3 x 3 x 2,500 = 22,500 gp.
The crystal mask of discernment giving an insight bonus is wrong wrong wrong.