Try searching for it on Craigslist...you have to make sure its the Hyperlearning series though, otherwise its just the regular PR Mcat review books. I lucked out and found the Biological Sciences Review book on Amazon and the Physical Sciences Review book on ebay for really cheap. I heard that PR people actively search and report people who try to sell their books on amazon/ebay.
I don't have the regular PR books to compare with the Hyperlearning ones, but the books should have the word "Hyperlearning" on it, so if you're wanting to buy and a seller doesn't specify which book it is...ask if they see Hyperlearning on the cover/spine or ask for a pic.