American Airlines has round-trip flights from Austin (AUS) to Chicago (ORD) for $97, NONSTOP. Flights August to December. Departures mostly on Tuesday, Wednesday, and Saturday. Origin/Destination reversible.
Note: Spirit may be offering fares for a bit cheaper, but you’ll want to avoid those since their pricing does not include a carry-on bag and has inferior flight dates. Spirit fares aren’t really worth it unless you can avoid the +$60 in baggage fees, which means they would have to be priced at about $37 round-trip to be comparable to the American fare.
Note: Carry-on bag is allowed for free, but seat selection has a fee. You can avoid paying seat fees by not selecting a seat and being randomly assigned your seat at the gate.
Click for more details and booking links Nonstop Flights: Austin to/from Chicago $97 r/t – American Airlines