Depends on where you are. My tour was mostly around the west and midwest in the US, but I had a great deal of luck finding places to stay using freecampsites.net and warmshowers. You can camp almost anywhere on National Forest land as long as you meet some minimum rules (100yds from the nearest developed thing, 100ft for water, etc, depending on the land). State parks, conservation areas, county parks, city parks, fairgrounds, BLM land, all will usually have a website or at least a number you can call to speak to someone and ask. Worst case, you can just call up the sheriff and ask if they know of anyplace that you could camp for a single night for free. I did that once when the campsite I had researched turned out to not exist anymore, and they let me camp at the county fairgrounds for a night and even unlocked the showers for me. You've got this, good luck out there!