American Airlines has round-trip flights from Chicago (ORD) to St. Louis, Tampa, Columbus, Indianapolis, Minneapolis, Detroit, and Cincinnati (STL/TPA/CMH/IND/MSP/DTW/CVG) for $97, NONSTOP. Flights August to December. No Sunday departures. Origin/Destination reversible.
Note: Carry-on bag is allowed for free on American Airlines. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.