Cost. Paying early termination on your rental contract. Paying to move. First, last, and a cleaning deposit at your new place. Stocking a new place with perishables. An easy 3+ grand to move to an inexpensive town.
Loss of salary/job opportunities. You won't have the same job opportunities, nor salary ranges, if you live in a less expensive part of the country, since your new pay will be based off your peers in your physical location, not your last salary in SF.