If cost is a consideration you might want to start in New Zealand or even South Africa. A DONE4 from Australia will cost you more than $11.5K, starting in NZ it will only under $9.5K, if you can start it in South Africa the cost will be down to about $7K (savings of almost 40%).

If you start in JNB you can do:
JNB-xMAD-VGO,OPO-xMAD-LHR-JFK-MIA-LAX-xSYD-DRW-xBNE-xSYD-JNB (the stop in DRW can be as long as you want as long as you get back to JNB within 1 year of starting).

So you still have three more sectors. You could use them to visit the Middle East (replace xMAD-LHR with xMAD-xxx-LHR) as well as two more sectors in North America.