If you are in Bangkok you can catch a bus from the EkamaiI bus terminal to Ban Pae bus terminal. The fare for this Bangkok to Ban Pae bus trip is around 125 baht and the trip takes approximately three hours.
A good speedboat service is the White Shark service from Ban Pae. White Shark is located at, one of the main jetties. I call this jetty number two, because it is the second main jetty you come to after arriving at the main promenade which runs along the waterfront. A landmark for this jetty is Ban Pae police station. The police station is on the opposite side of the road. almost opposite the jetty.
You can travel by speed boat across to Koh Samet for 200 baht per person one way. The round trip in the ferry is 200 baht each. There are other charges that you will incure if you go by ferry. The taxi fare (pick up truck) to your hotel and park entry fee.
When you take a speedboat to Koh Samet you will arrive on your designated beach. This is great because it means you don't have to ride in the bumpy pick up truck from the main pier to your accommodation. The roads on the island are still in bad repair, and the 2 or 4 km ride is very challenging for your spinal cord. Not having to ride the pickup truck also saves you time and money.