You can probably use the micro-V belts to drive the wheels - its wouldn't be too hard to make the one-piece hub & pulley from HDPE. Here are some photos of similar parts from my bots:



This is the J sized micro V pulley VS the old A size pulley. The micro V pulley can reliably wrap around a smaller pulley on the motor allowing my to use smaller & lighter pulleys. The micro V pulley looks complicated to make, but it just needs a simple cutter to be ground and accurate marking out.



This hub is from the horizontal spinner Demon. It only has one pulley but the concept is exactly the same as the drawing above.