Discover HomeCamper! (Private camping rentals)
Camp in private, unique areas for a low price or make your land profitable by hosting travelers from all over the world.
www.homecamper.com
The site seems to be populated by people outside the USA, but there are listings, so far the 2 spots I looked at have 0 reviews.
But there are a few spots that are $5-10/night which is great for rv boondocking.