Welcome to the RTA Forum!
I guess the best place for you to start would be to check out RTA's planning section and start reading up on the variety of tips that we've already provided. The art of the cheap roadtrip is one of the may articles I think you'd enjoy. There are also a number of threads dealing with budgeting on the forum. Here is a good one to start with.
I'll also throw out my basic advice for anyone who is planning to do a shoestring budget for a trip. It can be dangerous to budget unrealistically low, while living on peanut butter for a month sounds like a nice cheap idea, the reality is that if you try to do things too cheap, eventually you'll start to splurge, which can quickly blow and entire budget. It makes much more sense to set realistic goals that you can obtain, rather than put the enjoyment of your entire trip at risk by trying to cut too many corners.