Not sure how to explain it, but while the book has been out of print, it appears to be in short supply. The prices for used copies of The art of project management are hovering over $100 at amazon. And I couldn’t find a single copy listed on ebay. My guess is many folks hold onto the book as a reference, so despite the book’s sales numbers while in print, it’s hard to find.
The updated edition should be in stores and on amazon in a few weeks, so if you wait, you’ll save some cash.