US airways US to South Pacific Award
US-Thailand(Stopover)-Australia(Destination)-US 80k USDM
Thailand-Singapore-Thailand round trip 15k Avios
Australia-New Zealand-Australia round trip 25k USDM
AA US to South America Award
US-Buenos Airies-US AA Off-Peak Award 40k AA
Buenos Aires-Stantiago,Chile-Buenos Airies 15k Avios
Total:
105k USDM
30k Avios
40k AA
If you want to you can try to route back from Australia via South america and skip the last leg from south america to the US and save 20k AA miles.
Note prices are in economy, some are very worth considering for business/first e.g. the US award to south pacific can be had for 110/140 in C/F, and Aus-NZ-Aus USDM award can be had for 30k Biz.