Depends on your definition of best....
The cheapest fares will all require a one way ticket to another RTW starting point.
In the case of One World, the closest discounted starting point would be Japan (with a ticket that does allow passing through Australia) ex Japan a DONE4 is US$5589 PLUS taxes and airline add-ons. Starting in Australia US$9175 ++++ Add 50% to convert to AU$$.
May you find a way to do inexpensive wandering
Fred
Hint: flyertalk has a one world forum dedicated to the subject