Speed over Posted Limit: $fine + Demerits
0-9km/h: $75 + No Demerits
10-19km/h: $150 + 2 Demerits
20-29km/h: $250 + 3 Demerits
30-39km/h: $350 + 5 Demerits
40+ km/h: $1000 + 7 Demerits

Go more than 45km/h over and it is automatically classed as reckless driving.

More info at http://www.delonixradar.com.au/speeding_fines/