This 50-seat A/C bus is still operating but (IMO) is no longer “express.” This bus will take you from the BKK airport onto the Center Point Ferry and drop you off in Klong Son on Koh Chang—or vice versa—for 308 baht, which includes your ferry ticket.
We rode this bus between BKK and Koh Chang many times last year and it was fast, convenient and comfortable; stopping only in Chantiburi and Trat. But we rode this bus yesterday from Trat to BKK and they have changed the route. The bus now stops in Trat, Chantiburi, Rayong and Pattaya—not counting a 30 minute stop at a roadside restaurant for food, drinks and bus driver commissions—before continuing on to the airport. The trip took a full 6 hours from Trat—which is not express in my book—and had you boarded on Koh Chang, you would have been on the bus for over 8 hours! We were told the BKK to KC route is now the same, namely BKK—Pattaya—Rayong—Chantiburi—Trat—KC, so it’s hard to imagine it being faster.
The bus yesterday was full, so apparently the new route has increased business at the expense of being “express.” If you are returning to the airport from the islands via the Trat bus station, this “Express (not!) Bus” is scheduled to leave Trat at 3:45pm, but you may be better served by taking the Cherdchai Bus to the airport at 9am or 3pm, or the 11:30am #999 that stops at the airport on the way to Ekkamai. The cost from Trat to the airport on the Suvarnahbhumi Bus was 248 baht, and the website is: