If you don't mind buying them from Amazon, then there are these GE 70w ballasts for $22, the only issue with them is that they don't have mounting ears and the wires come out the back:
https://www.amazon.com/GE-87546-GEMH70-SLJ-MV-Halide-Ballast/dp/B001T23NBGThere's also this Sylvania ballast from Amazon for $45 that is more akin to a standard FCAN ballast:
https://www.amazon.com/Sylvania-51962-QTP1X70MH-Halide-Ballast/dp/B002OMC3A2Now I will admit that I've had mixed experiences buying lighting stuff from Amazon, but that hasn't been the case for ballasts.