Oh yeah - again from BKK .... to SIN for example, the second tiered carriers are the cheapest because they are not as frequent as SQ and Thai. So you can get BARGAINS.
SK - daily to Singapore. All fares return.
Economy Class - US$110
Business Class - US$236
SR - 4 times a week to Singapore. Return fare
Economy Class - US$145
Business Class - US$230 (special season)
For BA - one can only get specials from HK to MNL. The TPE fare is higher.
Cheers!