So, if we assume that it grants 9/5 of a feat (since it grants 9 skill points), that means 18000 GP. I did the math wrong earlier; it's actually a 17500 GP discount from the baseline. Subtract that from the total cost of the item for 19500, which suggests that WotC thinks that decreasing a score by 2 is worth compensation of 29500 GP, so each 1 point is 19750 (assuming it's linear, because that's the least broken interpretation since I plan to scale this up to 5). So, logically, you can buy a tome that decreases your Strength and Dex by 5 each and gives you a +5 Inherent bonus to Wis, and then be a druid and laugh because the game owes you 60000 GP. I'm being a bit silly, aren't I?