Since I've just been going through the same thing (almost same itinerary!), I can tell you my experience. I called travel agents in New York and they basically gave me the rack rates or a little less. The hotel websites give you "Internet discounts" which are less than rack rates. Most of the big name travel agents on-line (thaifocus, asia-travel, hotelthai, globaltravelexpress) do get good deals, some below the "internet discounts", but many simply give you those same rates from the hotel website. Some get better deals on certain hotels they deal more with.