GBA Flash Linker + 256mb cartridge + GBA NES Emulator + As many NES roms as you could think of.

I think, in the end, it works out much cheaper.

p.s. Yeah, like hell I'm paying for GBA games anyway, the only one I've bought is Boktai, because you can't play it on an Emulator anyway. That and it's awesome and worth buying.