Sydney is also considered hotspot by QUEENSLAND, I have written all these things to garp, only option is writing online which garp is planning from 2021I think you should write to GARP and explain your situation. I'd be very surprised if they didn't waive the fee for deferring the exam.
I live in Melbourne and am registered for the 21st November exam here. There's a decent chance I think the exam can go ahead in November (not sure about October). But I think interstate travel will basically be impossible before Christmas at the earliest. As you say, it is also likely to cost you considerably more to get down here (plus hotel quarantine at each end at your own expense) than the cost of deferring the exam, even if you do have to pay $150 USD (which I doubt you will).
Is there no option to take the exam in Brisbane? Sydney might be another option too.