Campervaning in the States
RVs will cost twice to 5 times as much for gas than does a car, but since there are some places to stay for free, and campgrounds are often at least half the cost of motels, it probably can be done 'cheaper' in an RV. Depends on how far you go each day and how long you stay at each destination.
With Passport America, I just got back from a 6 week trip at an average of about $11.00 a night. If I didn't need electricity each night, would have been a lot less than that (stopping at rest stops and such when just overnighting). Also saved a bunch cooking/eating food in the trailer rather than eating in resturants.
Before I needed electrical gadgets to sleep, I stayed in rest stops/truck stops and the like with never a problem, except for once when a cattle truck pulled as close to me as he could get, and the side of my trailer was decorated with brown specks...