mineralized skinfinishes are limited items, that have only been released, i think its 3 times total over the past few years. if you do a search, you can find more info on them, and also, there is a thread on them just halfway down the page, look around, you'll find some very useful information.
also, retail ranged from 22.50-23.50 from what i know, depending on when they were purchased. the last release of them was lingerie in december of last year. most of them are going for $40+ on ebay and in the MAC communities.