I just picked $75 because I used to see individual PDS discs listed for $25 online (quite a few over the years, in fact). If you were buying the missing one rather than selling the remaining ones that would round it off to $100 for a complete copy which is better than it usually goes for. I've seen the manual and case sell for more than 50 bucks. I had to get a replacement case and manual for my copy in fact, but I got mine for less.