From [[Surat Thani]] train station and Surat Thani Airport (URT), there are combined bus/ferry services to Ko Samui for 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. The cost should certainly be less than 300 baht, even if bought this way (return combo boat + bus ticket on more comfortable Seatran ferry bought on the Nathon pier on Samui officially costs 230 baht).
From Donsak pier, there are 2 ferry companies (departures every 30-60 mins) which terminate at Nathon Pier: Songserm Travel [http://www.songserm-expressboat.com/] and Seatran ([http://www.seatranferry.com/]. 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. The upper deck, 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 on-board shop on the lower deck, but the prices are grossly inflated (instant noodles, which cost 15 baht in a 7-11, are sold for 50 baht on-board). If you choose this boat, bring your own snacks. The people aboard Songserm ferry are mostly, if not all, foreigners.
Seatran ferry is much bigger, and 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), and is equipped with numerous TVs (Thai channels). It 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.com/schedule.php] (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 Nathon). It includes a free air conditioned deck and comfortable seats. This ferry also transport cars, so can be used should you decide to come with your own transport. 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 1000 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''' (+66 25 29 654 in Bangkok)[http://www.songserm-expressboat.com/en.php] 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 1,250 baht (1,000 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 longboat trip via 2 islands), and the ferry itself is comparable to Seatran, the entire trip 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.
