I live in a small class "C" RV with my Sherpa on the back.
In the 2 years I've lived this way I have only paid to camp once at Death Valley Daze last year.
I do dispersed camping in the forest or on BLM land or stay at one of the Indian casinos that let RV's park without hassles.
I just looked at my expenses for the last year and figured out that my monthly expenditures have averaged about $300 a month.
That's staying in the states and not moving around much with the RV, using the bike to run errands like groceries and laundry.
I spent 3 months over the summer near Flagstaff in a nice dispersed camping spot and not once did I see a ranger or other forest person so I stayed much more than the 14 day limit. When the weather started to cool off, I moved down by Safford and then to Tucson and the surrounding desert. Plenty of places to camp for free with nice weather.
I allow myself one restaurant meal a month, usually a Chili's or a pizza, otherwise I make all my own meals.
Since I'm not a social kind of guy, it works out well for me, I don't have to put up with anyone else, well, Bill The Duck visited my camp a few times and he is tolerable for a night or so and he shows up with tequila.
So, it can be done cheaply, it's attitude as much as anything. You'd be amazed at the things you can do without.