As mentioned above really, drill motors are a very simple an very effective source for drive. Ewan Gimson sells them at a good price, and he overvolts them in his robot at 18v giving him a very good reliable system (using the sdewinder speedcontroller). I guess you are looking at 4wheels drive? If so, then the simplest method of using all four wheels is probably to use four motors(wheels directly onto the motor gearbox)-espcially when a set of pulleys can cost more then the motors!
I would recomend using a 4channel 40mhz transmitter (futaba is always a good choice)as this will give you the option to add a weapon at a later date.
almost everything except the motors are now shock mounted in my robot, using rubber gromets for speedcontroller/baseplate mounting, and neoprene(or any good rubber/foam) for surrounding my batteries. Since i did this my robot has become MUCH more reliable.

Good luck