I am flying during Christmas too, from the 20th - 26th Dec.
Got the ticket this morning via the net, but I think any travel agent can offer you similar fare, as there are so many flights to SE asia everyday.
Next time you can go to
www.zuji.com.hk or
www.aerohkg.com to take a look before making any booking. Sometimes the travel agents can give you a better rate because they have group tickets for sale.
I am constantly looking for bargains too, but I found that I might not save a lot flying from Macau after I added up all the costs.
HK - BKK RT is around HKD500 if I manage to get the lowest fare. HK-Macau RT is around HKD300. Macau ferry terminal - airport RT (Express Link service) is around HKD100. Airasia charges around HKD400 taxes and fees for Macau-BKK RT.
Airasia operates a 'free seating' policy, meaning it won't assign any seat to the passengers. Anyone can sit anywhere he wants. You can imagine how messy it can be.