You offer only half of the story. What machine? If the PSU okay?, what's it's rating? (chances are it's matched to the drivers and the motors). Are the drivers okay?, what format is the controller? and how have you realised it's faulty?

Drivers? - tell us about your existing drivers.
Power Supply? - tell us about your existing power supply.
Steppers? - are these working?
Let's assume the controller it u/s.

If the driver, PSU and motors are all good then you might be able to get away with just a parallel-port BoB. And a dedicated PC, with LinuxCNC installed. And a Parallel cable.