We were going to drive out west this fall (RT would have been about 5600 miles) but instead we decided to stay on the east coast and hop around to some state parks in the Blue Ridge Mtns. ($20 a night), then down to the Smokies ($24 a night with full hookups and cable TV) for three weeks total trip time.
We'll do about 1400 miles RT on this trip. We prepare almost all our own meals so don't count that any extra cost than we would have at home. Even with the cost of gas, we're ahead of the game. It works out to about $55/day for our vacation for the both of us for gas and lodging. The only way you could do the same trip for cheaper is if you drove an economical car and tent camped along the way.
With our rig, we have most of the conveniences of home including internet access because we have a Verizon Aircard with an antenna booster for the more remote areas. And you don't have to live out of a suitcase or set up camp. You just pull in and plug in your power cord and hook up your water line. Then dump your tanks when you leave. If you had a satellite TV set up, which we don't at this point, you'd really have it all.
It really is the way to travel, but for the time being, we'll stick close to home to save money on gas.
Lest you think we're gas hogs, both of us work at home and we put only about 15,000 total miles on both our cars combined per year. People who commute can put more mileage than that on one car alone.