we camp a lot, 3+ months/year.
In small towns often a church, county fairgrounds etc. will let you stay for free for a night. In some small towns, we hit a local restaurant with large parking lot and they will let us stay overnight for free as well, course we do have dinner at the spot and sample the local fare. Often very good food.
Forest service, BLM, etc CG run $5-7/nightfor seniors, double that for non-seniors. BTW all it takes is ONE person with the "golden eagle" for the discount including extra vehicle discount. but usually no hookups, which we don't mind at all. Many have water and dump stations. Next are Casino's. CG are their "loss leader", and some 10/10/10 rated campgrounds are casino's (7 feathers in southern oregon) and with discounts etc. run about $20-$25max/night.
We can usually find nice RV parts in the $40 range.
Then there are the county campgrounds/fairgrounds etc. that run in the $20-25/night.
Then there are the Oregon state park campgrounds. While I love our state park campgrounds, very nice, lots of stuff for the grandkids to do, well located etc. they are at the high end of campgrounds for price. Full hookups run $35+/night, no hookups about $25+/night.
KOA's are at the bottom of our list. IMHO way overpriced for what you get.
BTW, in the last 3 years we've kept track of our RV expenses. Our total cost/day including fuel, campgrounds, food including occasional dining out, souveniors, entrance fees, etc. etc. averages $85/day.
We have a friend who has done 2 Three month around the country tours in his MH and he also kept track of all his expenses. His daily expense was in the same range, somthing like $88/day.
In both cases that's for two people, add a family and extra food is going to bump that up.