I second Raja's Fashions.
You will find many cheaper/faster places. You can hardly take a step along Sukhumvit Road without tripping over a tailor shop.
I had 3 sport coats made + a shirt and a few ties thrown in for about $150USD each. A sport coat bought off the rack in the USA of comparable quality would be $600 USD and up.
I would plan on at least 4 days and 3 visits. One for the initial measurements and 2 additional fittings. They will deliver the finished product to your hotel room.
I can't wait for my next trip so I can visit Bobby and his father again!
-woof