finding cheap multi-city airfares
 

I'm planning a 2.5 week trip to Cambodia (1 week for volunteer work) and then New Zealand (1 week fun), leaving from the US. I'm trying to find a way to put together an itinerary that would not be cost prohibitive or too time consuming (no more than 2 stops each leg). It looks like going thru BKK is a good way to do it but it is possible to check luggage thru onto Bangkok Air and will Bangkok check thru to a legacy, e.g., Qantas with separate tickets? any other suggestions?
Thanks for answers to any of the questions.

Bangkok Air should check through to any full-service airline. I know it checks through to Thai, United, etc. I've often been able to check through even with separate tickets... in fact, I can't think of any time an airline would not check my luggage through. Of course, budget airlines do not transfer luggage, even to their own flights, but Bangkok Air is not a budget airline.

Thanks, Kathie. Good to know about the luggage check thru - it'll save me some time. Will I have to go thru immigaration or can I just pick up the Bangkok Air BP in the airport without exiting & re-entering?

Right now it looks like the cheapest way to go is via BKK with a separate RT to REP on Bangkok Air. Still waiting for an air fare sale since I'm still a few months out.

Yes, you can pick up your boarding pass at the transit desk, airside. So no need to go through immigration.

You could also use Kuala Lumpur to fly into and then use discount airline Air Asia to fly to either Phnom Penh or Siem Reap and back. If you wanted they also fly to Australia from where yiu can catch a flight to New Zealand. The savings in cost outweigh the Inconvenience of not being able to check your bags through.

If you use Bangkok airport you can still use Air Asia to fly cheaply to Phnom Pemh and then take a bus or taxi to SR.

Try playing around with dates and destinations on kayak.com.
I've often had good luck on that site for piecing together itineraries.