As has already been mentioned, there aren't any all encompassing passes for camping but try these sites -
http://freecampsites.net/ Free and inexpensive campgrounds and boondocking spots. We've used many of them.
http://www.ultimatecampgrounds.com/uc/index.php/2012-10-03-01-10-22 All public campgrounds with a range of cost from free to kind of expensive.
You may be able to get away with using free WiFi hotspots. Check the visitor centers at National Parks. Sometimes they have it. Good places to stop at en-route are Panera Bread, McDonalds, Lowes and Home Depot.
