A 3h flight is going to be much faster than a 12h drive. It may be cheaper if you fill the car with people but will cost more if you do it alone. That's assuming you consider your time to be worth nothing.
Unless I'm flying a RyanAir flight that's under $100, a tank and a half of gas to go 700-800 miles is going to be cheaper, if we're sticking in the 12-hour drive frame. And that's driving a not-particularly fuel efficient pickup truck. Gas is only $2.09 this week.