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X-box One digital game prices from the X-box store differ by country/region and allows you to buy games in a different currency.
The digitalgamesprices.com website shows you the game price currency converted to the cheapest regions so the price is easily comparable (the cheapest price is flagged in green).
nb1 I am not affiliated with this website in any way. I found the website when I realized I could buy a game cheaper just by changing my region and restarting the Xbox.
nb2 Once you have purchased the game, set the region back to Australia (or whatever yours normally is) and play the game as usual.
Thanks OP! :)