You can easily control the amount you pay in overnight campgrounds by limiting the services you need. Camp at CAMPGROUNDS rather than RV parks and for the MOST economical (and also usually the most scenic) campsite choose one that doesn't have the three utilities (elec, water and sewer) since you won't actuallY need them for an overnight stay. MOST RV parks have a single rate and you'll have LESS control over the costs. Of course you'd always have the options many prefer, of camping in parking lots but when I travel I do so for enjoyment and that is FAR from enjoyable to me. To each their own.
Good luck and have a good trip / Skip