Freedom isn't Free.
Trump is demanding Tribute from all US vassal states.
The US has massive debt, needs to re-shore manufacturing & rebuild its military.
Investment from allies is a way to help with this.
Qatar had to commit $1.2T in a much smaller economy, so Australia got off lightly.
Trump is making all US allies who aren't pulling their weight militarily and would require US troops to defend them to pay Tribute in some form.
At least Trump allows it to be invested in things that should generate decent return.
In previous ages the Tribute was a cash payment.
It is a broken system that will collapse. There is no need to pay tribute to the US. The money would be better spent elsewhere.
Perhaps that Pine Gap early warning system sitting in the middle of oz should be rethought.
What are Australia's options?
Don't pretend that Australia can just continue as is without US protection.
It won't last long before someone else comes to demand tribute.
That has always been the way of the world.
Thucydides c.455–c.400 bc
History of the Peloponnesian War bk. 5, ch. 89
The thing is... I don't believe the US military would step in to defend Australia if it needed it.
Only if it was in their best interest to do so.