Spirit has round-trip flights from Austin (AUS) to Chicago (ORD) for $103, NONSTOP $52 each-way. Flights from mid-February to the first week of March. Departures on Tuesdays, Wednesdays, Thursdays, and Saturdays. Returns on any day except Friday or Saturday. Origin/Destination reversible.
Note: Spirit fares do not include a free carry-on bag. Only a small personal item, like a Jansport City Scout backpack is free. Checked bags cost +$30 each-way. You can avoid paying for seat selection if you accept the randomly assigned seat prior to boarding.
I’m currently using the Jansport Right Pack as my “personal item” when I fly Frontier. Which is slightly more than expensive than the Jansport City Scout because its fabric is Cordura instead of Polyester. Both have the same dimensions which are: 18″ x 13″ x 8.5″. There is half-an-inch of extra depth than what is officially allowed by Frontier, but it has never been a problem for me. The bag has a large main compartment, which makes it ideal for stuffing as much as you can into the limited amount of space.
Click for more details and booking links Nonstop Flights: Austin to/from Chicago $103 r/t – Spirit Airlines