AirAsia runs these frequent sales when you book 6+ months out. While the headline fares used to be low, the taxes and fees would make the flights just reasonable (not really cheap). Now the fuel surcharges have been dropped and things are a bit cheaper than usual.
The current sale has a lot of Southeast Asian destinations from Kuala Lumpur for very low prices.
The return trip to Langkawi prices out at $38. The return trip to Siem Reap comes out at $66.
Picture courtesy of royalcaribbean.com