YNP is a long way from almost anything else in Montana, I would not think about day tripping from there. I think we were quoted about that much for the KOA in Bozeman tho, I turned around and left and found a much cheaper spot.
We stayed at Bear Canyon CG which was about half that but just a warning. That CG is right off I-90, just to the south. There is an underpass THAT IS ABOUT 12' high. My son yelled just before we went under it. This means you can only get to the place if you are east bound on I-90 if you have a 5ver or any other high RV. It is certainly too far away from YNP to daytrip, something like 90 miles.