Having full-timed for 16+ years we have not found the cost to be as high as some of you state. It all depends on how expensive you want it to be. There are many, many ways to live comfortably.
We don't sit in RV parks at $30-$50+ per night. We move around and staying in public parks or boondocking are always our first choices. If you're 62+ get the Senior Discount card for public parks. You'll only pay 1/2/night and free admission. Volunteer for those very special national parks. You'll get a full hookup site free. We love doing that. Especially in the western states there are some beautiful spots to boondock for free.
Food - no different from a S&B house either by cooking your own or eating out.
Entertainment - if you're used to paying big bucks for a theater or concert ticket then you'll probably do the same while traveling. There are many free things to take advantage of and that's what we typically do. We love just being outdoors - hiking, walking, siteseeing.
You can do as much or as little as you want while full-timing.
We know many who can do it on $20 - 30,000/year. It's all up to the individual. I would advise anyone considering full-timing to have your RV and vehicle paid for along with any extra bills. Go into it debt-free.