Another less used option is your local Elks Lodge. Ours has room for about 15 units and is the cheapest around. It takes about a year to get a spot and then it's yours as long as you want. You do have to join, but yearly membership and storage fees are still cheaper than most places.
Even though some think an Elks lodge is for old folks, we joined and are involved in the lodge for some things, but we are now eligible for discounted camping at any of their lodges nation wide. They even have an RV guide that tells you about the parking at each lodge, the price and how many spots.
They're not always where we want to be, have what we would want to stay in or are available when you need it, but many have worked out nicely on long trips (overnight stops) and will have anywhere from 20 amps to 50 amps with full hookups for $10-$15. You can also bring a guest (another rig) with you.