Wow, I really appreciate the quick replies! My dilemma is that I will be moving to the Nashville area, and after hours of research, there doesn't seem to be many boon docking opportunities in the near vicinity of the city. The state parks and BLM land is quite a ways out from the city. Maybe it's a pipe dream to expect cheap/good sites near an urban area...
I definitely plan to spend most months at a regular RV site near the city, but if I could spend a few months 2-4 per year in a place where I don't have to pay close to $500 dollars a month in rent, that would be ideal.
There are a hand full of Army Corps of Engineers sites in the area. The nightly rates are in the $14-16 range. I can't seem to find and info about discounted monthly rates, but if they offer a solid discount, it could be an OK option.
Any other ideas to save a little $$$ and get off the grid while still semi-close to the city?