Please be aware that Taipei and Seoul has multiple airports and that these results are for all airports serving the city.
The best month to fly between Taipei and Seoul is April and the most expensive month to fly is May. (Average prices, based on 242 datapoints.)
The cheapest airline flying from Taipei to Seoul is Jeju Air. They are 48% cheaper than EVA Air. (Average prices, based on 251 datapoints.)
The best time to fly is at around 11. (Average prices, based on 277 datapoints.)