As stated, seriously consider volunteering. It makes you feel good about helping out and you'll get a nice campsite. You don't have to do it constantly. Many state park will take you for 1-2 months at a time. Then move on and do a little siteseeing before starting at another park. Many full-timers do this. Our favorite was giving lighthouse tours. Some people are hosts in the campground, some work in the visitor center, some on maintenance outside, etc. There are many different tasks.
As to campground costs - you've been given some good ideas on how to do it more reasonably. If you're not into swimming pools and lots of park activities, then don't stay at those kinds of parks. There are parks in all price ranges.
Pick your locations carefully and stay away from hot tourist spots....unless you want to do those things too...but it'll cost you.
Even in Florida there are some very reasonable places to stay. The Rio Grande Valley (RGV) in Texas is another reasonable place to stay. If you move further west you'll have some gorgeous areas with good prices.
The coastlines will be more expensive than inland. It's all about location.
Personally, we love public parks - national, state, COE, national forest, county and city parks. It's very easy to boondock is beautiful surrounding in the west. Mix it up. RV parks are not the only places to stay.
Good luck with your plans. We've enjoyed it for 16 years. It's a great, relaxing lifestyle. Remember...it's not a long vacation. You don't have to do things every day. Do what you normally do at home now. Don't rush your travels.