Yeah, $80 is about what this game is worth someplace like ebay, but if Gamestop is restocking with new items they should just sell them for $50 or maybe $60 and deal with the fact that they are going to get resellers buying it. (That's a common issue when you reprint a book, comic, or movie too). Not that you would expect either company to not screw over their customer.
That said, the trilogy is by far the best way to play these games, because the Gamecube control scheme is really sub-optimal. Personally I would have preferred a dual-stick shooter, but the games came out before that control setup was standardized. Prime one and two have an incredibly good sense of atmosphere, almost like Bioshock, and being able to have that weight invoked through a widescreen TV, with surround sound is amazing.