Da Du ja sicher nicht schimmen willst gibt es folgende Möglichkeiten :
***Boat Services to Ko Samui (Schedules and fares mentioned here are subject to change without notice. Please contact boat companies or TAT office in Surat Thani for current information.)***
Surat Thani - Ko Samui Songserm Rungrueang Co, Ltd operates express boat services from Surat Thani to Ko Samui. The boats depart from Surat Thani daily at 8 a.m. Travelling time is 2.30 hours. One-way fare is 150 baht. A joint ticket for connecting route, Bangkok-Surat Thani-Ko Samui, is available.
A nighttime boat leaves Ban Don pier (in Surat Thani town) at 11 p.m. daily. It takes 6 hours for the journey. One-way fares are 100 baht and 150 baht
Don Sak - Ko Samui Don Sak pier is located 40 kilometres from Surat Thani town. Racha Ferry operates ferry services from Don Sak pier to Ko Samui 7 times daily from 8.00 a.m.-7 p.m. It takes 1.30 hours for the journey. One-way fare is 55 baht. For more information, contact Racha Ferry at tel: 0-7737-1151, 0-7737-1026 (Don Sak Office) or tel: 0-7742-3026 (Ko Samui Office). Private vehicles can be loaded onto the ferry. Bus services from Surat Thani town and Surat Thani railway station to Don Sak pier are available.
Nun musst Du nur noch die Fährenanbieter " abklappern " und weisst genau wie Du fahren kannst 
LG
Sandra