I've been thinking of doing this too... was thinking of building my own controllers too!
I personally would go with two electric motors (A/C) and chop a DC voltage into pulses (PWM) so that you can control the frequency and therefore speed of the motors.
A couple things to keep in mind:
-With Batterys, you basically want the highest voltage (form serialing them) so that you don't lose out on line loss.
-Motor controllers could be constructed as simple as high amperage relays (solenoids) much like a winch controller.. They are mechanical and wouldn't last too long (they are based on the amount of cycles they go through)... they also wouldn't allow you to have speed control (also, if you go the DC route with DC motors you could control the speed by controlling the voltage... but unfortuantly this would not allow for high torque at no rmp).
-You can construct a controller using high amp mosfets much like the commercial types and control the speed (if DC) with pwm to get the high torque at low speed.. or for AC where your pwm circuit will generate the AC pulse and your mosfets would control the direction.