How much current do these motors draw? We got some Banebots controllers for $30 each, they are reversible, have a BEC that works to power a Vex signal splitter, and are very small. Low current....they are designed to power a motor at only 3 amps continuously, but they seem to work ok in the underwater robot the students built for the NURC.
http://banebots.com/pc/ELECTRONICS/BB-0309
Be very careful to get controllers that will go both ways with a single PWM input, if you need that capability...I messed up first time and ordered some that did not!