I have only ever paid for 1 scan in all 5 pregnancies and that was my choice to go to a private place for a scan. Not sure if it is different here in NSW. Can you ask your GP to do a open referral so you can find your own place to do a scan. Or ring around, some places take referrals that are not for them. Also one referral I got was from the midwives clinic at the hospital and it could be used anywhere.
Just some options that may or may not work for you.