I was just on Air Asia's web site and it looks like zero dollar fares are available again for numerous dates over the next few months. I just booked a SIN to KUL flight for 61 SGD on Feb 22. At this price point, it is competitive with the bus that I have been taking between Singapore and KL previously. Incidentally, according to their newspaper ads, it looks like Air Asia uses T1 at Changi.