Because you have stepper motors and drives, the only part you need, except Mach3 will be a rather simple bob. But try first Kay, maybe its good to handle.
Mach3 itself costs as much, but you don't need to rewire anything in the machine. But I don't know which stepper drivers are used in the machine.
I believe every drive can be controlled via step/dir maybe with 12V instead of 5 or with negative logic, but that all isn't really complicated.