I've been following the project for a year now and Clemens Elflein has actually managed to get the topic off the ground professionally. Recently, his kit is available, with which you can upgrade a cheap Yardforce robotic mower to GPS support. This eliminates the need to lay boundary wires.
Are you sure with the price of the lawn mower? The "yardforce 500 classic" should cost ~300 EUR = ~495 AUD mate.
I was including the shipping cost from Germany to Perth in the cost