Avianca has round-trip flights from Los Angeles (LAX) to San Salvador or Guatemala City (SAL, GUA) for $175-$188, NONSTOP. Flights August to November. Departures on Monday, Tuesday, Wednesday, and Sunday. Origin/Destination reversible. No Thanksgiving dates.
Some small OTAs on Skyscanner and Google have this for as low as $155; cheaper than the airline. If you plan on booking there, beware of any site that charges a fee to cancel a ticket within the 24-hour “free” period. Use unknown booking sites at your own risk.
Basic Economy. Only a personal item (17.7 x 13.77 x 9.84 inches) is allowed for free on Avianca. You can avoid seat selection fees by accepting the randomly assigned seat at the gate. Note that the personal item size is about the size of a small Jansport SuperBreak backpack.
It costs an additional $60 each-way for checked and carry-on baggage.