What is the local Thai brokerage commission?

It's 0.25% of the amount of stock bought or sold in Baht, or a total of 0.5% for the round trip on a buy/sell transaction.  (Plus the 7% VAT tax on that commission). Sometimes there is a minimum commission on smallest orders.   If you trade on line with a Thai broker, the transaction commission can be as low as 0.15%.  Beware that Thai stocks bought/sold outside of Thailand often have much higher broker transactions costs. (Commissions).