So if they expect to have 10,000 users (again ballpark) in New Jersey, but they instead get 40,000 they'll increase their costs. If they get 1000 users in say Wyoming, then maybe the costs in Wyoming will be lower.
The issue is they have a world wide capacity of 10,000 users at 11 MBs over the size of New Jersey. Again, I haven't run these numbers but these are the kinds of calculations GEO sats make to set prices for say, airplanes traveling from US -> Europe. The difference is that GEO targets specific areas more rather than blanketing the entire earth due to them being stationary.
The benefit of Starlink is that it'll have approximately equal signal all over the earth. So if you're in a city it can cover the same number of people per mile as it can in the middle of the ocean.