Please be aware that Bangkok and Seoul has multiple airports and that these results are for all airports serving the city.
The best month to fly between Bangkok and Seoul is June and the most expensive month to fly is September. (Average prices, based on 555 datapoints.)
The cheapest airline flying from Bangkok to Seoul is Jeju Air. They are 45% cheaper than Jin Air. (Average prices, based on 559 datapoints.)
The best time to fly is at around 2. (Average prices, based on 644 datapoints.)