Its been bugging me all night, I knew I remembered seeing this before.
Oh yeah, I made it back in 2010, huh.
Very cool. Thanks for the link. How did you come up with the price?
While my notes on this particular item are long gone, my modus operandi usually is that after whatever guidelines and discounts and the like I do the final step is always "but what level do I want this item to appear at", look at WBL, and price or adjust price) accordingly. Though, were I to reverse engineer this I'd probably justify it like this.
Alter Self is 2nd level. What spell level would I place a limited single-shape alter self spell (IMHO, 1st). This puts it in line with Disguise Self.
It is both more and less useful than Disguise Self in that you're limited to a single race (while a human could disguise as an elf), but more useful in that its a real transformation.
Just to be sure (and since I know the abuses with Alter Self, esp. concerning Outsider type) I limited the list to a short list of non-abusable humanoids, leaving out things like the natural armor powerhouse of trogdolytes or the possibilities of outsider shenanigans.
With all that in mind I found it comparable to Disguise Self and thus the Hat of Disguise, pricing it the same. I'm also comfortable with it being available the same time the hat is.