United has round-trip flights from Dallas (DFW) to Cozumel (CZM) for $268 with a connection. Flights January to February. No Friday departures. Saturdays only.
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).