Free or inexpensive campsites in or near southern Ohio?

Hi. I am looking for a free or inexpensive place to go camping within a 4 hour drive of Dayton, OH. I am looking for somewhere kinda of isolated with out RVs or tons of people near by. Somewhere where each camp site is hundreds of feet at least from the next camp site, not right on top of each other. An outhouse and shower would be preferable.