Ah, so small motors then. Not machine shop size motors for a CNC machine. Got it.
How are you controlling the motor speeds and directions? Do you have limit switches at the ends of the travel in your 4 axes?
There is probably a PIC or Arduino evaluation board that would let you receive RF in some mode, and would have motor control capability. Or you could use a more generic eval board, and build a separate board with the RF module and motor control circuitry on it (PWM H-Bridge?).
You might also look at hobby remote-control vehicle modules, to see if that works for you. I don't know if modules exist to let you control 4 channels simultaneously, but worst case, you use both hobby RF frequencies at the same time, with 2 channels being controlled by each RF channel.