We stayed here it is nice and they were not too busy. Daily is high but seasonal may be better
Rustic Wagon RV Campground & CabinsAlso that same site has videos of every single RV park and campground in West Yellowstone so you can check them out yourself
CampgroundViews.com Kind of like Google Street View for RV parks.
We have also stayed at Grizzly and that was expensive.
If you are willing to commute my personal favorite is
Henry's Lake State Park they have paved full hookup sites now! Probably have length of stay provision but if you are forced to break up your stays why not.
Also if you don't mind a dirty car and want to stay on the lake
Madison Arm does have seasonal sites.