For this bot I plan to use PVC that my brother gave me. It's 1/4" thick and most likely the same stuff sold here http://www.budgetrobotics.com/shop/?shop=1&cat=103 I am able to cut it with a razor knife, but I have cut myself a few times in my excitement to get a base mocked up. I'll try my Dremmel to see how it goes.
I went to Radio Shack and picked up some discontinued VEX motors. In reality they are nothing more than Futaba S148 servos modified for continuous rotation. That and they use the VEX square drive shafts and clutchs. At $9.97 ea I thought I ws getting a good deal ... though I'm not so sure of this. Servos are slow and 4' x 6' is a rather big field ... I am seriously considering using my old tank base with DC motors and encoders already mounted.
In an effort to play with prototyping a new wheel layout though I mounted 1.5" strips of Velcro on my cutout base so I could play with motor/wheel spacings. This is on hold as I'm brainstorming my ball launcher too much.
Tank base
Prototype Base. 8"x8"
Onward,
Jay