Go up to ~$100 and the choice of smartphones becomes even more diverse. Quality would probably be a bit better too. This is with no contract, unlocked everything (chances are it's also Mediatek based, which means no bootloader locking AFAIK), and you get all the features like dual SIM, removable battery and expandable storage that most of the big-name manufacturers don't want you to have.

Edit: actually, it looks like $50 is already enough to get a pretty good entry-level Android phone; look up the Jiayu F1.