American Airlines has round-trip flights from Dallas (DFW) to San Jose del Cabo or Montego Bay, Jamaica (SJD, MBJ) for $322-$378, NONSTOP. Flights August to December. Weekends available. Origin/Destination reversible. No Christmas dates available.
A Carry-on bag and also a personal item is allowed for free on American. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.