I have $650 1st class tickets on Viva Aerobus from Tijuana to Mexico City and back. I can change them to be in your name (there is a $105 change fee, which the credit can go towards) for any flights / dates on that route. I don’t think you can change the start/end location (but I don’t speak Spanish well enough to really understand.) There is a U.S. —> Mexico border crossing in the airport itself. Tickets from here to San Diego are only $40, and you can Uber to the Tijuana airport from there, or tickets directly to Tijuana are around $200-$300. You can also drive to Tijuana in a day and can park on the US side of the border.