I still can't believe the amount this game is pulling in. I picked up a sealed GH copy about three years ago for $10, to replace my beat-to-hell launch copy. I haven't opened it yet, and at this point, I'm seriously considering just dumping it.
Anyway, yeah, it's probably not going to happen. You'll either have to be really patient and really lucky, or just suck it up and pay the going rate.