Check around for other ultra sound places in your area. My very first one was where the Dr's surgery had 'links' to and I had to pay. Every other scan so far has been bulk billed as I found another place (much better service too) and my GP now uses them.
That's for dating scans. I will still be paying for 12 week scan, around $160 rebate gives back $70ish.
It does pay to look around.