We've done this before. It's pretty fun. Let's assume that you have some leftover parts from the season (CIMs, AM or VP gearboxes, a few sprockets (perhaps mis-matched) and some chain.
Make sure the wood for the frame is straight, and that it's a hard wood rather than pine. Ok, pine can take a little bit of punishment, but in my experience when you start adding weight on top of the chassis and then you do crazy things, the wood screws which hold the frame together start to strip out.
You can then cantilever your wheels via 3/8" or 1/2" dead-axle bolts through the 2x4 frame, and chain a gearbox to the wheels. Use one of the calculators in CD-media to figure out which motor, gearbox and chain ratio to use. You can get away with chain-driving only one set of wheels, depending on what surface this chassis will roll around on. Just be aware that the heavier the frisbee shooter, the more likely you'll want to drive all wheels since even hard woods will flex while cornering at speed.
Good luck
