Travelup is a good site if you expand your travel dates to +/- a longer time, it gives you a comparison grid and shows you cheapest around that time, across airlines. I've been to Melbourne with Royal Brunei, cheapest i have ever been on to Aus at £630 last November, but this is a dry flight so they are a good company if you don't mind a small brunei airport and to not have an alcoholic drink on the flight.