I have flown a lot in Thailand, but I just Checked the prices of flights from Bangkok to Kho Samui, cheapest I found was around 13,000 bath round trip.

Thai Air from Bangkok to Khon Kaen around 5,000 round trip, about the same flight time, so what defends these ridiculous prices them operate with?

Erm , maybe because they have the monopoly ( bangkok airways ) and also happen to own the airport

Because there is no effective monopolies and mergers commission in Thailand.

You can fly to a nearby airport for cheap and take a very pleasant ferry to Samui.

Because Bangkok Airways own the airport and do not allow anyone else to use it.

Just fly from bkk to surathani with air asia then 1h30bus+1h30ferry..and you re here :-)

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Seeing that the government wasn't willing to pay for the development of an airport at the time, and willingly gave Bangkok Air the monopoly in exchange that's fair enough.

The island wouldn't have developed as much (tragedy IMO) without it that's for sure, used to be much nicer when the only way to get there from BKK was a 15-20 hour overland+ferry trip.

Or, you fly to Chumphon and take the ferry to Samui

Overpriced and over populated now, badly spoiled, not worth the trip anymore......IMHO.

Supply and demand. Next.

Bangkok Airways have the monopoly.

You can fly to Surat Thani or Nakhorn Sri Thammarat and use the bus/boat option which meets the plane.