A 300 baht surcharge is levied on domestic departures, as well as the 500 baht surcharge on international departures. If you fly via Bangkok to an international destination the tax is only 200 baht as the Bangkok international departure tax is already included in your ticket ex Bangkok. These charges are not included in the ticket price.
By ship
From Surat Thani train station and Surat Thani Airport URT, there are combined bus/ferry services to Ko Samui cost 200-300 baht - some entail a 60 minute bus ride to Donsak pier followed by a 90 minute ferry crossing, others a 30 minute bus ride but the ferry takes extra time. Tickets are sold by numerous agents that meet each train and airport. Should cost certainly less than 300 baht even if bought this way return combo boat+bus ticket on more comfortable Seatran ferry bought on the Na Thon pier on Samui officially costs 230 baht.
From Donsak pier, there are 2 ferry companies departures every 30-60 mins who terminate at Na Thon pier: Songserm Travel (http://www.songserm-expre...) and Seatran (http://www.seatranferry.com/, the website is mostly in Thai, however). The first one is what you more often get if booking via the travel agency. It's a rather small ferry with two decks, often very crowded so you can't get the seat on the lower one if you come late and the upper, while air-conditioned, costs extra, so you may end up sitting around the pile of backpacks on the back of the boat under the sun, if you do not want to pay. There is a small onboard shop on the lower desk but the prices are grossly inflated instant noodles cup, which costs 15 baht in 7-eleven, was sold for 50 there, so if you still choose this boat - better bring you own snacks. The people aboard Songserm ferry are mostly, if not all, foreigners.
Seatran ferry is much bigger, has several decks entrance to most of the those, including air-conditioned areas, is free, much less packed just because of size still can be at peak times of high season, equipped with numerous TVs Thai channels, has a big cafeteria with much friendlier prices, such as 20 baht for the same cup of noodles, and the passengers are mostly Thai, as well as some expats and tourists. Their schedule can be found here (http://www.seatranferry.c...) the first list is departures from Donsak to Samui, the second is return.
Raja Ferry Port (http://www.rajaferryport.com) operates services between Donsak pier and Lipa Noi pier on the western side of Samui several kilometres south of Na Thon. It includes a free air conditioned deck and several comfortable seats. This ferry also transport cars, so can be used should you decide to come with your own transport. Without a car, however, there are less options for a transportation there, and songthaew/taxi drivers may be more reluctant to bargain. Songthaew transfer from the pier at Lipa Noi on Samui to either Chaweng or Lamai will cost 100 baht per person. Taxis will be more expensive, with initial asking prices of up to 500 baht.
Numerous ferry services are direct from mainland Surat Thani including an express boat 3 departures daily, taking around 3 hours and costing 150 baht and slow night boats taking 6-7 hours. Call operator Songserm Travel 252 9654 in Bangkok (http://www.songserm-expre...) for the latest schedules, which varies according to the season.
Lomprayah (http://www.lomprayah.com) offers a combined bus/high speed catamaran ferry service from Bangkok to Ko Samui which takes about 11 hours 5.5 of them by boat and costs around 1250 baht 1000 baht in the opposite direction. The bus pauses in Hua Hin and then stops at Chumphon, where it connects with the ferry, which calls at Ko Nang Yuan, Ko Tao and Ko Pha Ngan on its way to Ko Samui. While the route may be more scenic as includes the long boat trip via 2 islands, and the ferry itself is comparable to Seatran, the entire way to Samui will take more time, and will cost more too.
Lomprayah is a good if not exactly cheap option to get to Samui from Ko Tao or Ko Phangan, as well as a reasonable one to get to those islands from Bangkok. There are also regular speedboats and ferries of other operators.
By plane
Ko Samui Airport USM is a private airport originally built by Bangkok Airways (http://www.bangkokair.com), which is still the main operator and was for a long time the only airline with services to Ko Samui from Thailand until Thai Airways started in April 2008 to operate some flights between Bangkok and Ko Samui. They have near-hourly departures to/from Bangkok and tickets are expensive by Thai standards, with advance bookings costing 3000-4500 baht one-way, while a walk-in booking may be twice as much. There are also daily flights to/from Phuket for 2000-3000 baht, Pattaya, Singapore and Hong Kong; two daily flights from Chiang Mai but only one direct flight in the opposite direction.
A feature of the International Departure Gate is a courtesy corner which provides food and drinks for all passengers in a cosy sitting area. Awaiting boarding becomes rather comfortable with food, drinks and wifi provided.
In addition to Bangkok Air, Ko Samui is served by two flights a day from Bangkok with Thai Airways as well as by Berjaya Air (http://www.berjaya-air.com) and Firefly (http://www.fireflyz.com.my) from Subang airport a small city airport 30 minutes from Kuala Lumpur city centre and Penang International Airport in Malaysia.
Soon, Silk Airways will operate on a codeshare basis with Bangkok Airways as announced in July 2011.
Visa-on-Arrival and Visa-Free entry is available at Samui Airport for some nationalities - see Thailand for more information.
Ground transportation from the airport is readily available. A seat in a minibus for the 20-minute ride to Chaweng costs 120 baht/person; a faster taxi will cost 300-500 baht. Be sure to negotiate the rate to your destination before you get into the taxi since many drivers refuse to use their meters.
If you're a couple or a family, you'll probably be approached by some young women holding up signs of some of the higher-end hotels - they will ask you where you're staying, and based on the answer, offer you a free taxi ride if you promise to attend a presentation for their hotel's timeshare during your stay.
A cheaper but less convenient option is to fly to Surat Thani by Thai Airways and low cost airlines by Air Asia and Nok Air Depart from Donmuang Airport and connect by road and then ferry.Or fly to Nakhonsithammarat by Nok Air then take bus and catamaran boat by Lompayah