Our plan included volunteering.
We've found we love it. But we only do three months at a time or less. We love that we visit fascinating places and don't have to run around all day for three or four days trying to see everything before we move down the road.
Limiting ourselves to shorter positions does mean we can't get some of the highly desired locations - but that's okay.
It is not hard to average near $20-25 per night if (1) you or the spouse is over 62 and you use federal campgrounds at half price, and/or (2) you belong to Passport America, and actively work their discounts - along with other discount programs - Good Sam, Escapees, even AAA or AARP.
Our 2014 average for paid campsites was almost exactly $20 - for 132 nights - and we will have stayed 175 nights for no cash spent with volunteering by Dec 31.
We have not boondocked a single night.
We also averaged $0.378 cents per mile for fuel - traveling 6,564.5 miles this year.
Frankly, I'm more concerned about keeping the fuel costs within budget - because the only control I have over that cost is to travel less.