Delta and American Airlines have round-trip flights from Dallas (DFW) to Minneapolis or Chicago (MSP, ORD) for $137, NONSTOP. Flights April to August. Most departures are on Tuesdays, Wednesday, or Saturdays. Extended weekends available. Origin/Destination reversible.
A Carry-on bag and also a personal item is allowed for free on Delta. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.