What drives the cost up for a porta potty in a remote November 2026 location?

Got a quote for a standard unit at our hunting camp this November. It's 50 miles from town on a ranch road, and the ground is frozen dirt. The vacuum truck can reach the spot, but it's a long drive. The quote is higher than I expected for a unit that'll see maybe 10 people over a week, no food or alcohol. What drives up the cost for a remote location like this in winter? Is it the mileage, the service visit difficulty, or something else?