I'm planning on visiting Koh Tao to go diving, however I am after a weight harness before going diving. Rather than buy one in the UK and carry it around with me, I was planning on buying one while out there.
What's the availability of dive shops on Koh Tao, and around the Phuket area?
Are they well stocked, and how do the prices compare to the UK?
There's absolutely no reason to bring your own, or even buy one. Every dive operation I've ever been on in Thailand and elsewhere in SE Asia has had a big box of weight belts, usually on the boat itself, which you're free to use.
Most shops quote two prices for dives: "full kit rental" (ref, BCD, the works) or "tank and weights only". And since you have to pay for the tank anyway...
Phuket is not only the dive capital of Thailand, but a major worldwide center for diving. Online directories list as many as 50 scuba centers, many with retail operations, concentrated on Patong Beach. You will be able to find all the major equipment brands.
For something simple like a weight belt, you can expect prices to be competitive with the UK— which is to say they will be more expensive than what you can find in the US or online. Inflation and the fluctuating strength of the baht make it difficult to say for certain. I will say that of all equipment, a weight belt would be one of the last items I would purchase. Many modern BCs will include some sort of integrated weight system of pouches, but there isn't much variation otherwise. I have never heard of any operation that will not lend you weight for a rather nominal price.
I have not been to Ko Tao in a number of years, but it has far fewer operations than you would find on the mainland, and so you can expect prices to be higher.
After a bit of googling around in Thai. There are lots of diving packages in Koh Tao and the prices range from 1000 Bath to 12000 Bath (depends how far you want to go). Some of that includes accommodation and all the necessary equipments for diving.
Most of them listed that the equipment can be rented for 400-600 Bath per day. But that means you have to go with them on the boat.
I'm not a pro diver so I'm not sure how much you need for diving, usually when I go to islands in Thailand. I rented everything and that costed me around 500 Bath per day.
I would recommend Scuba Diving in Koh Tao over Phuket. Koh Tao is not only cheaper but way better because of being less commercialized (relatively!)
From what I have heard, Koh Tao is the 2nd cheapest place for Scuba diving in the world, so it is definitely going to be cheaper than the UK.
You will find plenty of dive shops in Koh Tao - You can look up for the best ones on TripAdvisor. I have personally used Roctopus in Koh Tao and would highly recommend them.
Since I went diving a long time back, I am not exactly sure about the current prices. I googled and found this link that says it would cost you around 3000 Thai Bhat for a single dive and 8600 Thai Bhat for an Open Water Dive course. (Source - https://www.ithaka.travel/blog/scuba-diving-thailand-complete-guide-beginners/)
