Dub body would be WAY too heavy. Plastic body should be just fine if you dont wreck
From what i can tell, the ones the guy is building and selling on ebay are totally custom built. They have more rechargable batteries, bigger motors, different gearing, suspension mods and steering mods. The GNs on ebay are cabable of 30mph, stock ones go 10 (which is actually pretty quick for these little cars!). Just the mods in those pieces let alone probably are over 50-75 bux, plus his time and effort in making the cars, painted the cars, and the car itself. So I dont feel 150-200 is out of line, I just wouldnt pay it obviously, I just make my own.
If you go to Radio Shack and check out the starter kits (50 Bux), youll notice the cars are 1/28th scale. He had to do something with the chassis to fit the wheel base of the Buick GNX and GN bodies. This is the problem Im running into on mine. Im having trouble scratch making a driveshaft that is longer that works w/o binding the drivetrain up. This guy obviously has it figured out

I emailed him and he has yet to respond. You can sink a lot of money into these things really quick, just like any other hobby.
The reason Im building mine is for the challenge, and because a local bar is going to start racing them for prizes (read: beer) on Monday nights. I figured what the hell, Ill show up in a Buick body and show them how its done
HTH