American Airlines and United have round-trip flights from Austin (AUS) to Chicago or Miami (ORD, MIA) for $149-$169, NONSTOP. Flights April to May. Departures on Tuesday, Wednesday, and Saturday. Extended weekends available. Origin/Destination reversible.
A Carry-on bag and also a personal item is allowed for free on American. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.