I have no idea about the actual surgery, but your PHI should pay for the hospital accomodation (minus whatever your excess is). They'll only pay a small amount of the anethetist though, so don't expect to get heaps back on that (ie: last year I had an epidural for my caesar, the bill was $1000. I got back about $400, between medicare and PHI).
I had an elbow arthroscopy last week, to remove a bit of loose bone, and I'm seriously wondering why I went private... $1800 for the surgeon (will get around $600 back), $350 for the surgeon's assistant, $500 for the anethetist, $500 excess at the hospital for day surgery, $500 to hire the physio machine for afterwards... the list goes on and on. No idea how long I would have been waiting for the surgery if I had have gone public though. Not sure if they'd have classed it as elective or not, if I'd rocked up at the emergency department, rather than going to my GP when I first broke it. I'm also about $400 out of pocket for the x-ray and CT scans.
Good luck, I hope the bills aren't as bad as you're expecting.