Going to need more info. Are going from the ground up or do you just need the controls etc? Do you need to modify the mechanics or added them entirely.

What is important to you:

Cost
Speed
Style
Off road
Copy a real car
Just something that moves.
Complex control ie many channels

How low is low, and what do you want it to do? You can buy an old RC car at a thrift store for a couple dollars... if the car doesn't do what you want, it's a two-channel transmitter/receiver pair, which you can then use to control the car using whatever parts you can find. Old printers are a great source of motors.