i would like to get the evening train to bangkok from surat thani trainstation. What is a good and inexpensive way to get there from nathon where I will be staying

your options are to buy a combined ferry/bus ticket at one of the shops opposite the seatran pier or just buy a ferry ticket and look for the appropriate bus once you land at donsak.

The last boat is 6pm. Buy your combined bus+ferry ticket to Surat Thani at the official seatran ticket office (end of pier) in nathon, for 240baht. There is no big bus from donsak, only a minibus waiting at donsak at end of the walkway at this time of night (buy in advance too if its oversubscribed and you havent got a ticket tough - they wont take your 100baht), also disembark the boat early because if your on the back of the minibus in the corner you'll have terrible neck pain as you have bend your head for 1~hr journey.

Seatran bus drops you in surat thani center at about 8.45pm, as you disembark taxi touts will ask you 'where u go', if there are other thais travelling to the station then you're in luck and its 40baht per person, else if you're a lone traveller its 200baht (fair as it quite far away - 15min/15km) usually in the back of a tut tut. There are no government buses at this time of time about and waiting for a regular taxi can take a while. Info accurate as of last week.

Agree with the above.

Be warned there are no facilities to speak of at the station and trains often run late. If you are getting a 1/2am train and it runs a couple of hours late you'll have 5/6 hours sat on a concrete bench.