Flights to Bangkok. Best price if you are in Europe, you will find on the travel search page Momondo.
As Koh Tao is an island and so small that there is no airport here,
you have to get here by boat.
From Bangkok there are three options in different price ranges.
* Taxis from Bangkok International Airport (price around 500 baht/car) to Khao San Road in Bangkok. Then purchase your bus and boat ticket to Koh Tao in a Travel agency or Lomprayah-office costs approx 950 baht/one way, depending on season. The journey takes about 9 hours to the pier in Chumphon, there you stopping for dinner and snacks. The boat trip from Chumphon to Koh Tao takes about 1.5 hours.
Schedule and more information is available at Lomprayah-High Speed Catamaran website.
Even Seatran Discovery run boats between the islands and the mainland, their website.
* We actually do not know how to take this option because we have never traveled by train. We think it’s easier to take a bus or plane. But We’ll find out some more information and come back when We know more.
* Flight from Suvarnabhumi Airport (BKK) with Bangkok Airways to Koh Samui (USM). Usually around a 4000 baht / person and route depending on season. Then High Speed Catamaran from Samui to Koh Tao with Lomprayah. You purchase tickets at Samui
Airport, usually cost 550 baht, which also includes the transfer to the pier from the airport. The boat trip takes about 2.5 hours.
* Or fly to Surat Thani and then day-boat trough Samui and Phangan or the night-boat directly to Koh Tao.