United and Delta have round-trip flights from Houston (IAH) to Minneapolis (MSP) for $137-$142, NONSTOP. Flights in September. Departures on Thursday and Sunday. Very few extended weekends available. Origin/Destination reversible. Some routes are mixed carriers with Delta inbound and United outbound.
Keep in mind that United charges a fee for carry-on bags unless you have the United Mileage-Plus Credit Card.