United and ANA have round-trip flights from Houston (IAH) to Bangkok (BKK) for $536-$548 with a connection. Flights in September, December, January, February, and March. No Weekends. Departures on Monday, Tuesday, Wednesday, and Thursday.
Note: Fare allows for a stopover in Japan for +$120 more. If you’re wanting to spend a few days (or weeks) in Japan before going to Bangkok, consider doing IAH-NRT-s-BKK-IAH. Example screenshot below.
Note: ANA tends to have better service and cabins than UA.
Note: Avoid Air China flights on these dates, they have long connection times and bad routing.