I've driven from San Diego to Seattle. I know that's 90 degrees off your journey, but some things apply:
get the state guide to motels for each state you're in, it will have vouchers for cheap stays (30 bucks for 4 people with breakfast thrown in?!) and phone ahead day by day so you can amble in interesting bits and sprint across dull bits.
Eat at mom'n'pops traditional diners whenever you can, proper American food is fattening but fabulous.
You are supposed to tip at bars, but if you're never going back there, save money by being extremely English and forgetting to tip! Half the time they are so fascinated by your accent you can get away with murder (in southern Ca., the mexican workers cannot understand a word you say which can be a good thing!)