look in the Phangan info for boat times..otherwise go to a taxi boat man I know the guys who work on no 21 and 31 and book it you will prob pay between 2000 and 3000 baht it will take about 20 - 30 mins on longtail...for speed boat about 5,000 baht 15 mins...
check out ferry times from Thongsala I think 7 is the earliest...
2000-3000 baht?! Are you sure you've got that right? That's extortionate.
We paid a couple of hundred baht in September last year.
Give you a tip.. catch the Ferry across (slow, but cheap), and catch a boat back at 3-4 am. After this, you'll have to wait for the ferry which starts at 8 am (?)
Don't get a room there, take minimum stuff with you. Every time you'll here a story of someone's room was broken into and they stole the ENTIRE SUITCASE/BACKPACK. ie: Passports, cameras (and saved SD cards), books, journals and all the important stuff that money can't replace.
Prices also tend to be double that in Samui.. eg: coca-cola, internet, postage.
Also remember that drugs are illegal, and they set up tourists by using undercover cops. I was offered twice (of course i refused!).
Be careful but have fun