I do believe that some tent camp to save money but I doubt that most RV with the same financial return. RVing cost a lot in various types of fuel and then of course there is the actual living accommodations. No matter how ya pay for it, up front or financed.....well you have to pay for it, lOL.
So when everything is said and done I suppose people RV for the comfort and ignore the cost because they feel they are worth spending their vacation time as they see fit.
I don't see camp site costs as particularly expensive but can't say if the cost of an RV has gone up substantially or not since I've never tracked the costs.