Whether or not that rate is par for the course depends. How many people are in your group? Many parks are based on double occupancy, so if you have 5 or six people, $75 is more palatable than if you are a party of two. Taxes in Montana will either be 7% or 10% depending upon whether or not the location has a 3% resort tax. That is going to add four or five bucks to that total. Finally, do you qualify for any discounts? There are usually discounts for seniors, military and either Good Sam or KOA depending on the park. You can usually also get a discount for staying 7 or more days.
One thing to remember is in Montana, distances can be huge. Savings of $5.00 or $10.00 a night can easily be eaten up by a long commute. You mentioned Emigrant, Montana. Emigrant is 30 miles away from Yellowstone and 25 Miles from Livingston. A round trip commute to either of them from Emigrant is going to take 3 or 4 gallons of fuel and an additional hour of time. Something to consider. The Paradise Valley is an amazing area, enjoy.