The MBX5T is a very solid truck. It's one of the best. The new MBX6T is due out within a few weeks. So your gonna find great deals on used 5T's. It would be better than any RTR. Even so, to add an engine/pipe, and radio w/ good servos is probably going to cost you more than $600 Tires alone are $70+ a set
for what it's worth the Losi 8ight-T 1.0 RTR is still one of the best deals around. Good engine, good radio, fair servo's, and a good price. It's going to be hard to beat that deal.
Have you looked at one of these?
http://www.amainhobbies.com/product_...ducts_id/12363
Leaves you a little extra cash for a radio or steering servo. They seen to get around the track pretty good also.