Air Asia's online currency converter is quite misleading even though they try to cover themselves by saying -
Note: The exchange rate used here is based on AirAsia's rates and may not reflect those of your credit card provider.
A flight Bali to KL return for example costs Rp1.024.000 and they convert that to AUD$100.
Actual international rates (check the sites) is AUD$125 AND that is a big difference.
So my advice is to check out their conversion rate before you buy as it may affect your decision to fly with them - fellow budget travellers beware.