I keep track of our long trips. For example. With our 2020 26XD class C on a Ford E450 chassis used about 1,350 gallons of gas on last years 9600 mile cross country trip. We spent about $3700 on gas.
That comes out to 7.1 GPM. The average cost was around $2.75 per gallon.
This year we are planning another cross country trip of roughly the same distance. So out of my new cowboy hat that I bought in Eagle Nest NM on our trip last year picked this years fuel cost as being around $3.75 per gallon. Roughly $1350 more this year. I suspect it will be more though. Anyway, This won't stop us from going, it just means I have work 4 days per week instead of 3 to make up the difference. Retired but healthy knock on wood! For me I like to plan ahead a little.
Oh I also added in another 10% of our campground costs, but that is another thread.