Of course, we belong to the Escapees organization. Dues with the Escapees are $60 a year and it costs us about $10 a day to stay at the various Rainbow Parks and Co-ops that we stay at along the southern tier of states and along the west coast. Boondocking at the SKP parks is also very cheap. Many of them let you boondock for free the first day and then charge only $2.50 per day beyond that. Many have a 7 day limit, but $2.50 for seven days is pretty cheap!
Then we also belong to PassPort America. PA now costs about $40 a year and you get 50% discounts on fees at participating parks. Many of these parks have restrictions, so while you may not be able to use them around holidays or some weekends, even just a few days at 50% gives you a very short payback on $40 dues.
However, our best deal is the Coast to Coast park we belong to. In order to be a part of Coast to Coast, you must have a home park.
UPDATE/5/14/03
Our last cost cutting parking option is boondocking either at a friends driveway or out in BLM land or in a big box store parking lot if we are traveling two days in a row. Free is a great way to reduce your camping costs!