Originally Posted by
Often1
This is a very bad idea. Either talk with your local insurer and determine whether it has an affiliate which will sell you a policy in the US or rent from an established car rental company and use their coverage. While insurance through a car rental agency is rarely good value, in your case it may be a great deal cheaper than what you are able to purchase through an affiliate if that is even possible for you.
Cheap and inexpensive are sometimes not the same thing.
+1.
And if the OP books via the Australian website of a major car-rental company, he will likely be offered an all-inclusive rate that not only includes third-party liability insurance, but also includes a loss/damage waiver for the rental car itself. Those rates often provide very good value.