I converted that to ~US$250 which sounds fair to me since it likely involves putting the car on a lift, possibly removing parts of the exhaust shield and removing/replacing the disk while supporting the transmission. The part alone could be AUD$100.

The rear disk is often just fine even when the front needs replacement.

If the disk disintegrates while running at high speed, the driveline could flop around and cause damage to the shaft tunnel which I understand also is near air-bag collision sensors which might deploy the bags.