I miss my TurboGrafX and TurboExpress... Those were truly awesome systems, 16-bit, only had to buy one game card, and you could run it on both machines. It's too bad that nobody else opted to follow that line of thinking. 🙂
If you don't mind an older system without all the uber famous games, the T-Express would be a decent alternative, and should be cheaper than a GBA. Some of the games for it still rock and I can't recall having seen comparative games since (I'm thinking Military Madness, and games of that ilk).