Business/First Class fares from BKK are the cheapest. These are not full published fares but agents' consolidators tickets that you can get miles on.

For example a Business Class return ticket to Singapore from BKK costs less than US$400.
From BKK to Seoul return, it's about US$900.

The best deals are the BKK-North American flights - BKK to California return in Business Class - US$1800. First Class - US$2600. BKK to New York - Business - US$1900 and in First, it's US$2800. Remember, no stop in HK either way!

Just FYI.