Considering that you have a rather nice truck and buggy, I'd have a hard time going cheap on the esc and motor.

What are you looking for in terms of performance? Are you going to be running on a track or just bashing?

A good place to get started would be with a Compro 16018 controller, a Neu `1512 2.5d (2000kv) motor, and a 5Ah 4S battery pack. Although I prefer to run the 8Ah battery packs, I believe that I do so at the expense of a bit of handling to gain the run time.