Used Pokémon GBAdvanced games go for $30 at GameStop.
Used Pokemon games are really expensive. >:| I love the used GBA case at Gamestop; I was able to get the second Advance Wars game for like $5 and the GBA Final Fantasy's for around $12. Well, VI may have been more like $20, I dunno, but still a lot cheaper than the Pokemon games. I know I paid like $30 for a used FireRed. You could probably get a NIB copy online for that price or less.
Although that's still not as bad as $50 for a DS game. Damn, that sucks. D: