Air Asia sells a certain percentage of tickets (I'd guess 25-50%) at the low P category. Usually 900 baht per way, plus some taxes. ($60 or so RT) I just booked 3 tickets from SIN-BKK this morning, and got a mix of 900 baht, and 1900 baht on the tickets, so $90 or so RT.
I haven't flown SQ, but amazingly Air Asia isn't bad. While you'd have to hold a weapon on me to take a WN flight, I'll gladly get on an Air Asia flight.
I also got tickets to Phuket for $34 RT (all in). Some amazing bargains.