I live in New York and am looking to do a RTW which includes Bangkok-Singapore-Oz-NZ. I need to go as cheaply as possible. Do you think OneWorld is the way to go?

Where can I find a website that actually lets me plan the trip thru OneWorld?

I have also found that I can fly to London and get my RTW ticket from there cheaper than going directly from NYC. Is this usually how it goes?

THanks so much.