Hi
If you are using RC PWM to control the speeds, you can look into hobby type motor controllers. These controlers are light weight, small, and high current. They vary from 25A to 90A
with a simple 25A the costs are as low as 30 dollars, and with 60amps average are about 80 dollars. These are small controllers that are used for electric airplanes. You will find that these ESC's are light weight and very small but highly efficient.
Though if you want it to be bi directional, then you will have to find an esc for cars, and not planes.
I get my sources from
www.amainhobbies.com
Heres the link esc for cars: click the Electronic speed controller icon.
http://www.amainhobbies.com/index.php/cPath/1_221
And heres the link to the escs for planes/helicopters:
http://www.amainhobbies.com/index.php/cPath/2_389_416
http://www.amainhobbies.com/index.php/cPath/3_437_541