I was trying to find the sources to prepare my coming papers for various WWI topics and accidently stumbled into this, and it seems is free. John Keegan, in his book "The First World War", had mentioned that Australian official history for WWI has, comparing with other official history of all participants, a human dimension that none others have, so I feel perhaps some people here would find it interesting, particularly it is 100th anniversary of begin of WWI this year.

On the other hand, the website also has free version of Australian Second World War Official History.