It all depends what you have.
If you own a company it may not be straight forward.
If you just have a bank account and some stuff like a car or motorbike you can download templates
or simply right your own will in your own words and have it registered at the local Amphur for a very small fee.
On average a will done by a good lawyer (covering all legal assets )should not be over 10 000 baht.
I had mine done a few years ago for 8000 baht and it covers all aspects including the cremation.
Probate will be 30 000 baht and it can also be done by anyone for just the legal fees but it can be a little bit of a headache during already stress full times.
Remember the moment you die it will be illegal for anyone to take money from your bank account
and it is there for wise to have some cash available for the 3 months it takes to go thru the court system.
We bought some gold that can be turned into cash very easily.
It gives me peace of mind to have it all arranged and it will make things more easy for the people who stay behind.
Another thing to remember is ,anything in Thailand will be dealt with under Thai law,a will from another country is meaningless.