@Brenda5,
If you are'nt bothered by being slightly dodgy you could tell your GP you're suffering terrible headaches and chronic back and chest pain. If they put "headaches" on the referral that will get you a free brain MRI.
The gap for the chest, abdo, pelvis should be about $200. That get's most of you done LOL.
The boob specific one is harder to swing unless it comes from a "specialist, consultant or OPD at the hospital. No medicare if referred by GP and the price around here is $595 but seems to vary depending on the radiology place.
@CRM is that a public hospital? If referred by the surgeon you should not have to pay. Unless all hospitals are not operating that way...I'm not sure.