I stayed at
Valley View RV Park about 13 miles outside the gates of W. Yellowstone for about three months. This is a Passport America park. I paid either $300 or $350 a month (30amp f/h/u) plus $20/mo wifi, can't remember which rate. I think 50 amp is slightly higher but not by much. Roomy sites, no trees, a very large laundry/office. Gas station is next to the campground. Not a lot to do there but I only used it for R&R so wasn't a problem for me. I liked the park and will stay there again when I'm in the area. I stayed during the summer and left the first part of September. Traffic into WY was not a problem but I usually got there early.
Cat Lady