Couple years ago we were out to Yellowstone and stayed here
http://www.yellowstonevalleyinn.com/Yellowstone Valley Inn. About half way between Cody and the East entrance to Yellowstone.
They have a motel and campground there. We stayed in the motel. Shoshone River runs by the property.
Very nice place. Awesome breakfast. Just outstanding. Friendly folks running the place.
You'd be about 33 miles from the East Entrance. Gorgeous Drive.
Current summer rates are in the $140 per night range.
I thought highly of the place. Would stay there again. Did I mention the breakfast is awesome?
If you are in the Cody area go here for supper.
http://www.thecodycattlecompany.com/Chuckwagon buffet and great entertainment. Triple C Cowboys. Can't recommend them highly enough. Very much worth it. World class. No kidding.