diburning
AlcoHaulic
Have you given any thought to a 12 volt battery, 12 volt DC motor, and a chain to drive the "cart"? The battery could go under your seat, the motor could drive the front axle. If you wanted to get elaborate (not that I would want to), you could probably cobble together a regenerative braking system, kind of like you'd find on a diesel electric locomotive.
Get a position switch and hook resistors to it then hook it to the motor and battery. Instant notched throttle.