Neat. I paid $20 for my copy maybe 4 years ago, then sold it on ebay last year some time for $83. Of course, this is after I ripped a copy of the ISO to my HD... same thing in the end, since I didn't play it very much in the first place!
In the end, $50 is good, but without manual, $40 sounds ok. Though if you're getting a version to add to your collection, I would pass on it without a manual...
True story: Walked into a Gamestop last month, saw Disgaea 2 for $25, bought it with Edge card. Walked out, noticed it had no manual (you can't really tell with Gamestop until they give it to you), and walked right back in and returned it, 5 minutes later. Shrug.