The June trip was short - I just went down for a friend's wedding.
I did a trip at Spring Festival in 2012 which cost over 50,000rmb for the two of us, but I paid for the air fares with air miles, so that would be extra - maybe another 5000rmb per person. We spent a week in the Whitsunday Islands and a week in Sydney. We stayed at hostels and tried to eat quite cheaply. We did some expensive things like taking a ride in a small plane over the Great Barrier Reef and saw an opera at the opera house in Sydney.
It seemed that prices were much higher in June, but I was only in Sydney. I think with 20k each for two people you could manage two weeks, but you wouldn't get some of the experiences that we had.