Welcome to the forum, @Mjjeje - ask away on any question .... or click on the 'Discussion' button & then write in the 'search section' any word or topic you may be interested in. You will find terrific support & information here, from those who have gone before you xx
If there is a Medicare Number on the referral, I believe it is usually bulk billed?
If you are on a pension or have a Centrelink card, it should be bulk billed (but I had to pay about $180 when I had my Biopsy last Dec, which involved the Dr doing the biopsy plus a technician doing the ultrasound as well.)
All the best with your US xxx (Maybe, ask them if you've got 'dense breast tissue' - it is good to know!!)