There is no good way, they are all messy and involve hazardous substances. The best idea would be a new body, your health is more worth than money. If you need to strip a body of paint that's no longer available, I have heard of a product named "paint killer" by Carson. Miniature wargamers mentioned...
I've heard that redcats are pretty good, I think that there are quite a few upgrades for it out on the market but it you want total customization, then I would say save up for an axial, or a traxxas because both are very good crawlers.