We lived in Estes Park, CO - right next to Rocky Mtn NP - for 8 years. Although expanded a little now with Fall visitors (we called it the season of the newlyweds and nearly deads), it was basically a 100 day season.
We, just like the visitors, had to pay the highly inflated prices for even the basics like food and fuel. One guy told me one time that if I did not like his summer prices go someplace else - and then laughed. I never spent another penny in his place and told many people about his attitude and they did not go there either.
We would gather our lists of needs and make trips 35 miles down the mountain to Loveland and shop.
As has been said - it is the way of the world in tourist places with tourist weekends / seasons.