United has round-trip flights from Austin (AUS) to Sacramento, St. Louis, El Paso, and Kansas City (SMF/STL/ELP/MCI) for $114 with a connection. Flights June to December. Very few weekends available. Origin/Destination reversible.
Note: United “Basic Economy” fares do not include a free carry-on bag. Only a personal item (like a small laptop bag) is free. Seats are randomly assigned for free prior to boarding. If you have the United MileagePlus credit-card, use the “free checked bag” perk.
Note: The personal item size on United flights is smaller (9-in/10-in/17-in) than Frontier or Spirit (8-in/14-in/18-in).