The trick is to pick up many short segments and fly a roundabout itin on a fare sale route. Try AUS-DFW-STL-ORD-SFO and back for 7k Q-Mi, for about 200+tax. Of course, you'll need two days for the RT. I once tried to add ORD-MKE-ORD to make it 9k but there aren't enough flights to MKE.