You should also make sure you have enough spare cash to put yourself up in a hotel for a couple of unplanned days in case the weather turns to ugly to camp.
+1
Also, a little reserve for the unforeseen equipment failure or a new set of brake pads or a tire. Also there are incidental expenses like laundry, stove fuel, etc.
We tend to use RV parks quite a bit, especially in the eastern part of the country where public campgrounds are scarce. Generally, they have not cost more than $20/day. A lot of the RV parks also have laundry facilities.
staehpj1 is right about the small town city parks and fairgrounds in the mid-west. Stop at the store (usually a gas station/convenience store) or the local city hall and ask about camping. We were not on an ACA route for our cross country tour, but we found plenty of camping this way.
While facilities may not be fancy, some city parks even have showers or a swimming pool complex nearby.
Sometime you don't even need a restaurant
Good luck with you venture!