OW RTW ticket in business class, starting in Melbourne or Sydney (then Asia, Middle East, Europe, USA, Australia
Depending on your specific route, a Global Explorer ticket might be less expensive. For example, an IGLOB26, which allows up to 26,000 flight miles and books into I inventory (typically the cheapest and most restrictive business class fare) is $10,499 AUD base fare, and a DGLOB34, which allows up to 34,000 flight miles and books into D inventory (still discounted business class inventory but generally less restricted than I) is $11,999 AUD base fare, same as a DONE4. As mentioned, various taxes and airline-imposed fees are added to the base fare. The amount of which can vary quite a bit depending on which airline does the booking and which airline's flight codes are booked and which airports one uses. If you can offset the trip to start in Tokyo, a DONE4 would be $9,952 AUD base fare.
A basic route syd-hkg-lhr-tlv-lhr-lax-mel is roughly 28,418 flight miles. syd-nrt-doh-mad-dfw-syd is roughly 26,871 flight miles.