I'm not sure but elkitten may have put some reference to that in her thread I made a sticky LD.
Do recall on another thread she also made some comment for there appeared to be a significant variation, possibly $480 mentioned and elkitten did shop about a bit and may have got one for about $180.
I imagine it could also depend on where in the US you were and what local medical charges are generally.
I am going to be calling to book an appt. to hand deliver my PMV application to the AUS High Commision in Ottawa in about the next 2 weeks (and hopefully get an interview at the same time). I am not sure, should I book and do a medical now or wait for it to be requested? From what I have read and understand, in Ontario, Hamilton is the city where all the certified doctors are to do the AUS Visa medicals?