I previously lived in Asia for an extended period of time and have experience with tailors in a few different countries. The best price/quality I found was at Tailor on Ten in Bangkok. Ordered a bunch of shirts and one suit and am very happy with the final product. Was very easy to communicate with staff as the two brothers than own the shop are native english speakers. Their suits go for around $350 and obviously can spend more or less depending on your choice of fabric.