Southwest Airlines offers select 1-way fares to Mexico and the Caribbean with prices starting at $119.43. (Click on "Southwest Airlines" in the top line to see this sale.) That's the lowest rate we could find for select fights by $31. This price is valid on flights departing from San Antonio, TX, (SAT) with arrival in Mexico City, Mexico, (MEX) on April 8. Book this travel deal by March 5 for travel from April 7 through May 20.