$100 per night is out of my price range... If you want to be next to Disney with all the amenities I guess that is what you have to pay.
I have been to Yellowstone many times and have never seen a RV rate anywhere near $100, more like $20 a night..
I stay at a National Park campground in the Teton National Park which is about 8 miles from Jackson Hole and driving distance from Yellowstone for $10 a night.. No showers or hookups but with a RV you carry that with you..
Yellowstone
http://www.rvparkreviews.com/regions/Wyoming/Yellowstone_National_Park.html