American Airlines and Korean Air have round-trip flights from Dallas (DFW) to Ho Chi Minh City (SGN) for $873 with a connection. Flights February to May. No Weekends. Departures on Monday, Tuesday, Wednesday, and Thursday.
Some small OTAs on Skyscanner have this for about $843. 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.
A Carry-on bag and also a personal item is allowed for free. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.