Liran, ferry round trip costs 400 baht if you leave from Had Rin to Big Buddha Pier (45 minutes), 600 baht if you leave from Thongsala to Seatran Discovery Pier Bangrak or Lomprayah Pier Maenam (20 minutes).
No, any time you re-enter within the "enter before date" on your visa sticker, you will get 60 days.
When your last 60 days are going to expire, even if your enter before date is past, you can get a further 30 day extension at any Immigration office (1,900 thb)