Not sure about costs but MANY states have 'rustic sites" with no hook ups that go for as little as $4.00 per night. Also, Kansas, for example allows overnight parking in Roadside Rest areas. There is a special part of the park for just this purpose and it has picnic tables with shelters, free dump station and fresh water is available. Some also offer free WIFI and all for no charge. Just don't build a campfire or anything like that and usually they expect you'll be out fairly early in the AM.
Also when traveling through many rural parts of the USA small communities offer free camping with electric and water (a few also offer sewer) in order to get people to stop and stay the night. The assumption is that you may buy something (meal, fuel, etc) while there. "Don Wrights guide to free and under $12.00 camping" publication lists MANY of those type of sites along with nearly all government campgrounds and a FEW private RV Parks where they meet the criteria in the title. This publication comes in two volumes (one for East of the Mississippi and one for West of the river). I don't leave home without them.
Good luck / Skip