So around September-December, i am planning on making a few trips to the SE Asian countries such as thailand, cambodia, vietnam, etc.

I am doing this because i heard its cheap to fly out of HK to go to other asian countries. Its also cheaper around that time since it is post-summer traveling.

But recently i looked on expedia and orbitz and the listed prices were all over 500usd! This is NOT cheap! So my question is, is it really supposed to be cheap to fly out from hk? Is it cheaper than 500usd to fly to HCM city or bangkok? If they are cheaper, does that mean you have to personally go to these local travel agencies?

You should check local travel agencies. US based travel sites are no good for travel in asia.

As far as I know and in the past, it was cheaper to travel long haul to Thailand - and of course cheaper to also go short haul from there as the distances would be shorter from LOS vs HKG.  This may NOT necessarily be true any longer as the Thai Baht had appreciated quite a bit and THB quoted fares may not be be the cheapest in US$ terms any longer.

But the fact that Thailand is in SE asia itself and that as such distances would be shorter to another SE asia destinations - should make Bangkok your natural place with which to initiate your travels around SE asia.

Also, Thailand and SE Asia is home to most of the Budget/discount airlines vs Hong Kong which is a hub for a lot of major full fare airline - and thus it would be cheaper to NOT originate from Hong Kong.

And BTW - to get these cheap Budget airlie tickets, you'd need to go DIRECTLY to their websites and NOT via any travel agents.

Just IMHO

SEAJ

Stop booking through those websites!

If you're flying throughout SE asia, there are only two airline websites you'd need.

Cebu Pacific Airways
http://www.cebupacificair.com/

Air Asia
http://www.airasia.com/my/en/home.html

SeaJ, are u saying that i should first travel to thailand and then from there, use it as a hub to connect to other countries? Which are these direct Websites youre talking about? Are they the ones furryfriend is talking about?

Yes - IMHO you should fly directly to Bangkok and make this the hub/place you should fly oput of to other SE asian destinations via the budget airlines.  Another thing to Bangkok's advantage for you is that hotels, eating etc are way much cheaper than Hong Kong

Besides those that furryfriend mentions, there are other budget airlines like Tiger airways, One2Go, NoKAir, LionAir, Jetstar etc.  Google these budget airlines and go directly on their websites to book your cheap tickets.

SEAJ