Another thing to consider, is a 1/8 scale buggy like this one
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXAXV1&P=0
That Ofna is pretty decent for the money. You can have loads of fun with the buggies off the track too.
You could also look into a Truggy (basically the same thing as the one above but with longer A-arms and much bigger tires).
You could always go with a Revo 3.3, but those are too expensive. On the other hand, they are so popular that the parts can be found in any hobby shop out there.