For a rustler, you'll need a fairly small system.
I'm helping teach a camp where we use a low power, small sized basic stamp (BasicX24-p) to run GPS.
The ideal setup, as best I can tell, would be:
Car + speed controller (servo if gas, ESC otherwise)
basic stamp and development board
GPS receiver
use PWM from the board and GPS/compass via serin/serout of the shift commands to control the speed/steering
toss on an IR sensor or two, and you're ready to go!
Btw, I ended up getting a good deal on the maxbotix sensors. I picked up 12, and think I'll do 8 over 180 degrees (front) and 4 over the back. I was thinking I might use a BOE and a stamp for my inputs, unless anyone has a better idea.
I love my Phidgets interface kits, but each can only handle 8 inputs. I'd be looking at a minimum of 13 inputs at this point, and potentially 21 (12 sonar, 8 IR, 1 potentiometer).
What's out there in my price range? (that'd be 'cheap'
)