The more you plan, the less you pay (as long as you stick to the plan). For example, checking the local papers and visitor's bureaus of the towns you'll be passing through can shake out valuable coupons. Facebook, Twitter and coupon sites can also be useful.
Likewise, instead of depending on roadside attractions like the $100 gator wrestling class at Colorado Gators Reptile Park in Mosca, Colo., to meet your recreation needs, plan ahead to take advantage of frugal entertainment along the way. A good stop for frugal options is Recreation.gov, where you'll find inexpensive suggestions for fun like hiking and visiting museums. Depending on your route, you might consider pre-purchasing a national park pass or other recreation discount passes.
Speaking of your route, consider doing enough research to make a shorter trip fun. While 750-mile days, just you and the open road, may sound fun at first, most road trippers agree that they get old quickly. Short driving days are cheap days, especially if you can combine them with inexpensive recreation like natural and/or historical sites.