Travel from Bangkok to Koh Chang by bus 999. Someone shared an info so quotes:

“It probably was written before, but I just made this trip and thought I would share.

Last week, I caught a 999 government bus at 7:45 (pictured) from Ekkamai bus station to Koh Chang. It also runs every day at 9am, which arrives on the ferry around 14:30.
The bus left on time, stopped once for a short break and arrived at 13:00 on the ferry. Costs 261 baht per seat, tickets can be bought at the Ekkamai stand (pictured) from 6:30. You get a bottle of water and a small snack on the bus. The seats are comfortable and the bus doesn’t travel well over 80 km / h, so you feel safe. There is a toilet on board. Take a friend or buy 2 seats in the season if you do not want to sit next to a stranger for 5 hours.

You must carry your luggage high up on the ferry on the side stairs and take it off at the disembarkation.

You’ll also have to pay 80 baht per person for the ferry to KC (45 minutes), then 50-150 baht per person for the Songthaew taxi (open pickup with 2 long seats, luggage on the roof, Songthaew means “two rows” “) from the terminal Centerpoint Ferry Koh Chang to the hotel depending on where it is located. This is perhaps the most “risky” part of your journey, because you often have to squeeze into an overcrowded songhthaew. They won’t leave until they have 12 passengers, so sometimes you have to wait for the next ferry or offer more. I recommend putting on the mask as a lot of exhaust as it goes uphill.

Only 15 minutes to Whitesand Beach (50 Baht), 25 minutes to Klong Prao (70 Baht) and 30 minutes to Kai Bai (80 Baht). Maybe 40 minutes to Lonely Beach (100 Baht) and a bit longer to the Bang Bao ferry (150 Baht).

If your center is located on the eastern part of the island, you should arrange transport with your center, because taxis go east only 3 times a day; 9.00, 11.00 and 15.00 with Ao Thammachat, and soon after with Centerpoint. The cost is 100 baht per person.