Proximity to an airport is likely the first area I would compromise on. If I have to drive 4 or 5 hours instead of 1 or 2 hours to get to a decent airport a couple of times a year then that's not a big deal.
What I did look at last night was pricing of flights to Europe from various airports - there's some pretty big variation there. Denver seems to be about the cheapest at around $800 but SFO is not far behind. Boise was expensive at $1,400. So if I flew to the UK once or twice a year that could be a $600-$1,200 additional annual expense. Just one more thing to take into account along with real estate taxes, income taxes, insurance and all those other things that vary from state to state.
I just booked flights for a trip to England and Scotland in September and am flying out of Toronto for $750 instead of Detroit at $1,250 even though Toronto is a 4.5 hour drive vs. Detroit at 1 hour. Not sure if that makes me smart or cheap...