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Cheap flights to Australia are not too uncommon but not on full service airlines like Virgin which include bags, meals and seat selection. Previous deals. Dates seem to be February to September.
Melbourne via Virgin ($330 RT) - Momondo - Google Flights Use Google Flights to find the cheap dates and then plug them into Momondo or Skyscanner.
Sydney via Air NZ or Virgin ($382 or $393 RT) - Google Flights. Virgin includes bags, meals, seat selection whereas Air NZ doesn't.
I believe Scotts got it wrong, they assumed any international flight with AirNZ is full service so includes meal, seat selection and bags. This is not the case for AirNZ for any Australia or Islands flights, they charge for everything.