Equivalent to Band in a Box?

I'm looking for something to play backup tracks, so that I can solo over them, or practice melodies with backup. I've used Band in a Box in Windows before -- and that would be perfect. But, it is VERY pricy, and, I was hoping that Garage band would do something similar.

Does anyone know if it is possible to input a set of chord progressions, style of music, etc, and have garage band play backup for me?

Let Me know!