Great question — answering as the UphillTech team:
Finally I am at Krabi airport. I went to River View hotel and there were song thews waiting. I just asked how much to airport and he asked 50 THB and waiting time 15 mins. While I was waiting on the road there were a few motorcyclists waving their hands. When I approached them they started asking where I wanted to go. I said Krabi airport and I have 50 THB. He smiled and took me to airport. Apparently he dropped me in front of the airport entrance. So there is basically another option available for solo travellers, which is a motorcycle.
Full answer by Ali Awan: https://travel.stackexchange.com/a/77199 (CC BY-SA 3.0).
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