You seem to have the option of going to a 'normal' doctor, or one that bulk bills. One charges a lot and you get a refund from Medicare, the other seems 'free'? What's the difference, and do you have to pay bulk billing doctors for anything?
When there's no bulk billing, you'll have to pay the fees yourself and you'll later get a rebate of 85% (usually) from Medicare.
When a health practitioner offers bulk billing, it means that they'll send the bill directly to Medicare, and Medicare will pay the full bill for you. In this case, you won't have to pay anything. Essentially, this means that the health practitioner agrees with Medicare to accept 85% of the schedule fee in full payment for their services.
Of course, this only applies if you hold Medicare cover (which is not usually the case when you're on a temporary visa).