When asked this question (which comes up frequently), the biggest, easiest answer is: If you plan to move frequently, NO. Gasoline will eat up whatever savings you may reap from the less expensive camping options.
The other extreme end of this is, I once figured out that if we boondocked exclusively on BLM land and didn't move around a lot, we could spend no more than $400-something per year in "rent". (Don't remember the figure now.)
Two possibilities can make this a very affordable lifestyle:
(1) I've been told that America The Beautiful passholders (62 and older) pay only half price for all Corps of Engineers parks, but that's all I know about the COE parks.
(2) If you buy a used TT membership ($1000-$3000 usually, depending on terms, plus a $750 transfer fee), after that large upfront cost, your camping generally costs you nothing more than a $500-$600 annual maintenance fee, which can be paid monthly if desired (so, max $50 per month) and allows you to go straight from one TT park to another, 365 days a year. The main downside is that you have to move every 21 days (with some contracts, if you pay a $29 fee you can stay an extra week).
Of course, you'd have to factor in the gasoline cost to move from one park to another. But, at least here on the Left Coast, there are concentrations of them, so that you can easily drive less than 100 miles to the next park.
Buying an old TT membership is
complicated. Please start here:
http://www.rvlove.com/2015/01/28/thousand-trails-membership-upgrades
One cost that will be higher that you might not be considering is internet access, if it matters to you. Say bye-bye to unlimited bandwidth; you will never see it again. Technomadia is the place to go for all things mobile internet (
http://www.technomadia.com/2014/08/how-we-keep-online-illustrated-tour-of-our-rv-mobile-internet-setup/).
Hope this helps with your decision.