The Banebots controllers seem to work fine on ROVs driving bilge pump motors....
http://banebots.com/c/ELECTRONICS
We are using prototype four channel motor controllers from Cathode Corner on our ROV for the NURC this year. My brother designed them just for us...not sure what the final price would be on them....
http://www.cathodecorner.com/esc4/
I'm sure David would get a chuckle out of someone inquiring, though!
david@cathodecorner.com