Tailor Pro on Sukhumvit road. Great workmanship -- I went to tailor pro, but they were so busy I didn't really get a chance to talk to anyone (they just gave me the fabric book and left me with it).
Your budget and timing is reasonable (depending on the fabric you choose). I ended up paying $250 for a suit (cashmere wool Super 120s) with an extra pair of pants and 3 shirts.
If you have a particular style in mind (I really wanted a modern, slim cut suit with hand stitching), bring an ad of a suit you like (GQ has plenty of them) so you have a basis from which to choose. Here is the site www.tailorpro.net