I was just looking at something at Wiggle and stumbled across this. If it's been posted before, forgive me, but it's news to me.
A DhB branded Australian Standards approved helmet for <$70:
There are a few decent lower cost helmets floating around now, which is good. There's the Kali MTB helmets at Velogear, the Ranking helmets at Cycling Deal and the keenly priced Carrera jobbies at TBSM and elsewhere.