FYI, & to just take a look with an eye for my future use at the campsite link posted above, I looked at my area(and I know it very well!) which is in the middle of Daniel Boone Nat. Forest. There were a couple of forest campsites listed. There are many,many others besides those so my point is to say that the list seems it's limited by who posts a new campsite so not a very broad listing. JamieZ also seems to have a knack for finding the freebie sites, see the sticky.
A lot of the freebie/low cost sites boil down to shower vs. no shower but also give more likely privacy plus being truly in the woods as many RV'rs will avoid them because they lack the "nice" stuff.
"If I had my life to live over,I'd dare to make more mistakes next time...I'd relax,I'd limber up.I'd be sillier than this trip, take fewer things seriously, I would take more chances... take more trips...climb more mountains...swim more rivers...eat more ice cream." Jorge Luis Borges, at age 85