Yes. Domestic use is a tiny fraction of all water usage. However, as you point out it is necessary to incorporate the food water to determine actual water independence.
600 AUD/ML is ~400 USD/ML. The Sorek B plant in Israel is profitably contracted at ~0.40 USD/m^3 [1] which is comparable. That is one of the largest plants with cutting edge technology and one of the cheapest prices I have seen in my research. A quote of 600 AUD/ML for desalinated water right now in Australia seems a tad questionable, but not outside of what is possible. 2-3x that number is almost certainly believable (though they almost certainly do not have bulk scale) and would only increase the costs to 1.5% of GDP.
600 AUD/ML is ~400 USD/ML. The Sorek B plant in Israel is profitably contracted at ~0.40 USD/m^3 [1] which is comparable. That is one of the largest plants with cutting edge technology and one of the cheapest prices I have seen in my research. A quote of 600 AUD/ML for desalinated water right now in Australia seems a tad questionable, but not outside of what is possible. 2-3x that number is almost certainly believable (though they almost certainly do not have bulk scale) and would only increase the costs to 1.5% of GDP.
[1] https://ildesal.org.il/sorek-b-desalination-plant/