I don't know any good cheap brands, but I got a blued 13-round magazine from Mec-Gar for $30. The fit, finish and function are all perfect, and I didn't feel it was too much to pay for a reliable magazine.
EDIT: Evidently, the prices have dropped! CDNN has the same blued Mec-Gar magazines for $20. If you can get Mec-Gar for $20, I wouldn't even bother trying to find anything cheaper.