I'm not sure about the NT scan as we didn't have one, but depending where you go you should be able to get bulk-billed for the 19-week one. Blood tests also should be bulk-billed via your GP.
If you want extra scans or 3/4D ones, then you may have to go to a private billing place. I can't remember what we paid for our 19-week scan the first time - must have been somewhere between $100-200.