You are right about there being some bargains on AirAsia. Apart from the $25 SIN-BKK flight I am doing with my girlfriend, we are also booked on a $10 fare from BKK to Chiang Rai. Then after Laos, we are booked on a $7.50 fare from Udon Thani to BKK.

I then fly to Brisbane on QF but she continues on AirAsia from BKK to Penang, Penang to KUL, KUL to DPS, DPS to KUL, and KUL to BKK.

In many cases, these flights are way cheaper than both the buses and the trains.