Xanax is on the PBS, so if you are an Australian citizen or an Austrailan Permanent Resident or from one of a short list of countries you'll be able to have your prescription filled quite cheaply (likely less than $20.00). Your health insurance will not, I think, help you with the pharmaceutical bill (this might be wrong, check with Bupa).

As to getting a prescription, the drug is listed as 'Authority Required' which means that the prescribing doctor (and you) need to jump through some hoops to get it. The doctor will likely ask a bunch of questions to satisfy herself that you fit some criteria, then make a call to a government authority while you wait to get approval to prescribe it to you, then fill out a fancy prescription form.

Go to any old general practitioner in a medical centre, take the bottle and any other documentation you have with them (that'll help satisfy them that you meet criteria) and you should be OK. In some cases they might refer you to a specialist if it's a particularly fancy drug. In any case, you need a GP to refer you to a specialist, so you've gotta visit a GP first whatever happens.

Once you have that form you take it to any pharmacist, prove (if you can) that you are entitled to PBS pricing (with a medicare card).

The pharmaceutical prescribing system in Australia has a concept of 'repeats' where one prescription can be refilled multiple times, but that's not permitted with this particular drug (see the first link I've given, above).

I'm not really sure how to find prices (apart from just asking) for drugs if you're not entitled to PBS pricing, but there are lots of generics listed for that drug, so I imagine it won't be too frighteningly expensive.

I'm not sure how useful the health insurance will be for this sort of thing. You'll need to check what the policy covers.

I hope this helps.