For getting around there are really only two options, the regular Sawngthaews that constantly patrol up and down the coastal strip, or renting a motorbike. Motorbike rental is the cheaper option, at only about 150 Baht per day (plus fuel, but you only use a limited amount). The Sawngthaew will usually not charge less that 50 Baht per person, no matter where you are going, so these costs will add up if you are a group of more than one, and you go to three or four places per day. Traffic is light on the island, and reasonably slow, and the motorbikes are low powered and fully automatic, so it is about as safe as motorbike riding for the inexperienced is going to be.
Sightseeing is limited to a half a dozen waterfalls around the island, that are quite spectacular at the right time of year, and an excellent elephant park called Ban Kwan Elephant Camp. Also, there are some excellent jungle walking opportunities, from beginners to very challenging.