If you have a Five Below local to you, you might want to check them out. They have a number of GBA titles available right now. My local one has Paws & Claws Pet Vet, Disney's Aladdin, X-Men - The Official Game, Spider-Man 3, some board game collection, Chicken Little, and I think one other one. They also have one DS title, I think it is called 'Boogie' or something like that. It is one of the rhythm games. Not bad for $5 each.
Also, one of my local FYE stores had all their used games for 75% off, but I do not know if this is chain wide, so YMMV.
JY