I had all my personal dive gear,bcd regulators, 2 dive computers, and a  mask shipped usps from Florida to Koh Pha-ngan. It cost me 210$ to ship. It weighs 10 kilograms. I insured it for 3000$. I got a piece of paper saying I have to personally go to customs in Koh Samui to receive my package. I have no idea how much they will expect me to pay to receive my gear. How do they determine prices? Does anyone have any experience with this? Any information will be much appreciated thank you ???? 

Nobody will be able to help you with this question, they can come up with any formula they like.

 

I do recommend to do it yourself and not use an agent. An agent will not lead to lower prices but will incur a fee.