Unlike the old bus station of Trat, the new station (built 2007) is not located in the center of town, and you’ll need a taxi to take you to the markets/guest houses area.
You can take a Songthaew (literally “two rows” – Thai shared or chartered taxis) or a motorcycle taxi. A ride to the center shouldn’t cost more than 30 Baht (20 is preferable, but sometimes it depends on the number of people on the cab and the greediness of the driver).
If youre going to Ko Chang, you can take a taxi from the station to the ferry. If you decide to charter the taxi, it should cost around 150 Baht. If there are more people, it should be around 50-70 Baht. The ride takes 30-40 minutes.
Getting to Trat from Bangkok: aircon buses depart every hour (more or less – this is Thailand) from Morchit (northern) and Ekamai (eastern) bus stations in Bangkok. Service starts a 7:00 AM and runs till 23:30 PM. Sometimes there’l be more than one company selling tickets for different buses, so check out which one of them leaves sooner. Sometimes there’ll be toilets on the bus, and some comapies include cold water and a snack in their price (it should cost around 200-300 Baht). The ride takes 5-5.5 hours. The bus stops on the way for food and toilets..
If the bus breaks for some reason (broken aircon or some other technical problem), don’t be alarmed. The bus company will send another bus. These are the advantages of using a government bus, opposed to using a scam bus. If you took the bus from Morchit or Ekamai, you’re on a government bus (actually, private companies who have contracts with the government). If you took a bus from Khaosan road, it’s a scam bus. There’s no government bus station around Khaosan.
Getting from Trat to Bangkok: The above timetable (BKK to Trat) applies for the opposite direction.
Note: if you want to go to suvarnabhumi airport in Bangkok, take the bus that goes to Morchit station and tell the staff you want to get off at the airport.