Firstly just relax. I know, easier said than done, but it is worth trying. You have already had two children so must be doing something right. Medicare is FREE. Every single thing that the doctor requires you to have is FREE. Sure, you might have to wait for some things, but nevertheless, remember that word FREE. OB - whatever visits you have at the hospital will be fine. Shared care - this is okay if you are comfortable with your GP and feel you can afford it, or you have a health care card. But if not, midwife care at the hospital is fine ... oh yes, and it is FREE. Becuase you have already had 2 cs, they will probably want you to have another one, this is the health profession's way of ensurnig that they have as much control over the birth as possible - perhaps you could ask for a 2nd opinion.
Take care, look forward to hearing about your happy, healthy and cheap pregnancy!