Here in Victoria most of the opens have between 100-200 riders, normally spread over 3 grades. A few years back I used to ride the mid week crits at AFL park we used to have between 20-50 in A grade. Most of the other grades (B-D) had about 50+ riders in them. Numbers arnt everything, you will find the racing here is as tough as anywhere out side of Europe.
Ask Mr Hunter about it, he's been over here a few times ;D