I know that you can buy a pass for New Mexico State Parks for camping. Its $225 for a calendar year and you can use it at any state park, dry camping would be free and $4 for electric sites. But NM camping is pretty cheap, like $18 a night for developed sites so would have a spend more than two weeks there for it to save money. Utah Senior passes are pretty cheap, only $35 but they only cover day use sites. When we were in South Dakota we only went to one place that was state and that was Custer State Park and we took the kids swimming, all the rest of the sites we visited were National.
