United and American have round-trip flights from Austin (AUS) to San Jose, Costa Rica (SJO) for $317-$353 with a connection. Flights February to May. Very few extended weekends available.
United’s “Basic Economy” fares do not allow for 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.
The personal item size on United is smaller (9 x 10 x 17 inches) than Frontier or Spirit (8 x 13 x 18 inches).