There's lots of good information here but I don't think anyone has mentioned Thousand Trails. There's no telling how much money our membership has saved us but it's a lot.
Try to pick up a used membership - one that gives you park-to-park and at least 2 week stays. This last year we traveled to the northwest and worked our way down the coast, basically moving from one TT to another. Some of them are great, most are average, and a few something less.
You can't beat the price. Once you have the membership you pay annual dues that differ in amount based on the membership you get. Our dues are around $600 a year and we get the first 50 nights at no extra charge (some campgrounds charge an extra $3-5 for 50 amp hookups). After our 50 "free" nights we move to paying $5 a night for the rest of the year.
There are many different contracts out there, so someone is bound to give you different numbers - but all in all, it's a great deal for touring fulltimers.
Last year we averaged around $11.33 a night including all campground membership fees and overnight stays. I think our 2014 numbers will be the same or a little less. I'll be posting my 2014 expenses in my blog (linked below) after the first of the year.
Good luck in your planning.