In Koh Chang, you can always find shared pick-up taxis in main road which is not as same as metered taxis in mainland. They usually charge you as a person, the price is negotiable if you are wit group. Conversary, they charge you more if you are alone in a taxi. Here is the usual price to get to other towns.
Pier (100 Baht)
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White Sand Beach/Pearl Beach (50 Baht)
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Chai Chet (50 Baht)
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Blue Lagoon (start)
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Kai Bae (50 Baht)
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Lonely Beach (100 Baht)
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Bangbao (150 Baht)