I've been looking in the internet (yahoo, travelocity), and it seem that a circuit Thailand ? Cambodia ? Vietnam ? Laos would be rather expensive.
Is there a cheaper way to get flight tickets?
Thank you.

If you're coming from the U.S., you may want to check out Malaysia Airlines' AcessAsia Pass: http://us.malaysiaairlines.com/access_asia.html

Or you may simply want to buy a ticket roundtrip from the US to Bangkok and buy an intra-asia air pass or separate tickets. For instance, Bangkok Air, which services Siem Reap, Cambodia, Luang Prabang, Laos, and a couple of destinations in VN has an excellent "Discover Asia" pass.

Thank you!
I don't live in the US (I'm brazilian).
I'm looking for an intra-asia air pass, so I'll take a look at Bangkok Air site.

Remember you can usually buy an open jaw ticket for the same price as a simple round trip. Then get a separate one-way multi-city ticket between the arrival and departure cities.

For instance, we're going to Bangkok in late October and returning from Beijing (free r/t ticket on FF miles). From Bangkok to Hanoi to Hong Kong to Beijing in Business class all the way (with access to each airline's Business Class lounge is less than $600 US.

The Malaysia Airline Discover Asia package (or something similar) sounds as good as last year's program by Cathay Pacific. I have no 1st hand knowledge about Malaysia Air but Skytrax gives them a 4 star rating (VERY good)

Dale & Kathy
Baton Rouge