Need a good dc motor driver?

Hi all I have a quick question. I have a couple DC drill motors and gear boxes and I wont to make a robot. I am looking for a 20ish amp motor controller. I either need a dull one of two single ones. What do you all recommend? It needs to be able to plug into a regular receiver since I am going to be using a Dx7s and a simple dsmx receiver. I could be biger than 20 amps just I thought 20amps would be a good base line. I want to find something cheep like under $50.
Thanks!