The Twin Cities have enjoyed fleeting affairs with budget airlines in the past. AirTran provided dirt cheap flights between MSP and Chicago (as low as $59 one-way) for several years. When they left, fares rose considerably. For many people flying out of Minnesota, Northwest is the only game in town. A search on the major booking web sites last week turned up fares of over $500 between MSP and O'Hare. In short, Northwest has travelers trapped in a corner and seems intent on extracting as much money. Sporadic service by budget carriers like Sun Country has done little to alter the trend of high prices. But a deal between Twin Cities Int'l and Southwest Airlines will bring some significant change to the air travel market next year.