It only takes a few stays to pay for the membership. All RV parks in the program are private owned and they have a nice directory (which is out of date as soon as it is printed) but you can keep it up to date by checking their website. The use in the south during the winter is a little limited as the RV parks like to make more money then, while the RV parks all fill up. I stay and one RV park in Vidalia, LA a couple times a year and just 2 visits pays for the pass. Most campgrounds will limit the number of nights you can use it, usually 3 nights is the most, but there are always exceptions and a few have no limits on the stay, depends on how popular they are. If you plan quite a few trips it is well worth it.
Also if you are 62yo or older get an "America the Beautiful" pass for a one time (lifetime) fee of $10 to give you free admission and a 50% discount for campsites at most government parks, Corps of Engineer campgrounds and other National parks and lands, also some state parks. A few other perks like discounted admission to museums and historic sites (not 50% though).
Since you live in Georgia you may want to get a "Friends of Georgia State Parks" membership that I believe is still $35 for the year for seniors. It gives you a 20% discount at state parks (usually around $22) and you get one free nights stay, so the membership costs you about $13 for the year. There are some very nice state parks, Georgia Veterans State Park is a favorite.
2014 Palomino Puma 25RS
2011 F-150 Super Crew XLT
Days camped in 2014 - 23
Camped 2015 - 47
Camped 2016 - 51 done - 6 more planned so far