Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Koh Samui to Istanbul as you normally would.
2 stops31h 30m
Istanbul Sabiha Gokcen
3 stops25h 40m
3 stops39h 10m
For a flight from Koh Samui to Istanbul, you will be flying from Ko Samui. Ko Samui (USM) is just 3.3 km from the centre of the city. Ko Samui is the only Koh Samui airport and it handles 0 outbound flights to Istanbul per day. 0 airlines have flights to Istanbul from Ko Samui on a regular basis.
On average you can expect to pay ฿52,995 for a flight from Koh Samui to Istanbul. The cheapest flight overall is ฿51,757 while the most popular route, (Ko Samui - Istanbul Sabiha Gokcen) is currently priced at ฿32,241.