United Airlines has Brisbane, Melbourne and Sydney, Australia on sale at prices under $600 round trip from LAX and SFO for travel from next week into late 2019. Low fares are widely available every month through October 2019, except January and July.
American Airlines and Oneworld have similar fares from San Jose SJC to Brisbane, Melbourne and Sydney and low fares from SFO to Brisbane and Sydney.
LAX – Melbourne $582
LAX – Sydney $594
LAX – Brisbane $613
SFO – Melbourne $596
SFO – Sydney $604
SFO – Brisbane $616
SJC – Melbourne $604 (AA-Oneworld) – if these fares do not price for your dates through Google Flights, then try Skyscanner or Momondo.
SJC – Sydney $608 (AA-Oneworld)
SJC – Brisbane $637 (AA-Oneworld)
United Airlines Los Angeles LAX – Melbourne MEL – LAX nonstop
United Airlines/Qantas San Francisco SFO – Sydney SYD – Brisbane BNE – SYD – SFO
American Airlines San Jose SJC – Los Angeles LAX – Sydney SYD – LAX – SJC