It could be out-of-print. You'd be surprised how much hard to find music can cost, especially if it was originally a limited production run with few discs made.
I paid $60 to buy a copy of King Kobra III off Ebay a few years ago. I had seen it for sale at $270 so I got a relatively good deal.
Tommy Shaw (of Styx) first CD with the song 'Girls with Guns' is long out of print and hard to find and I've seen it go for nearly $400. I got lucky on that one too, got it for about $30, but it is the re-release on a different label and not the 'original' version.