Yeah I could move 3 hours west and double my salary in Detroit, but there's a reason salaries double when you move that direction.
Because you're moving into a crime-infested hell-hole?
3) Gear from 85 to 90 doesn't leave you in a position to go to heroics, even if you get all the gear available.
This is not accurate. The "Heroic" dungeons are basically the entry-level lvl90 dungeons. You do not need specific item levels to queue for them or complete them.
I think that you are thinking of the Challenge Mode dungeons which are designed to be very difficult and so you probably will not have adequate gear for them when you first hit 90.
The easiest way to figure the cost of living is to take your income and add ten percent.