linux.conf.au (LCA) has been running 10 years now and draws over 500 attendees.
This is the pricing table from the last LCA:
Professional / Hobbyist / Student
$795.00 / $375.00 / $125.00
Open Source Developers Conference (OSDC) has been running 6 years and draws closer to the 300 mark. From memory tickets were $325 aud.
Web Directions South has attracted over 500 attendees since 2008. Pricing info here.
I should note that LCA's numbers are high because many attendees fly into the country for it.
Sydney vs Melbourne is tough. Both have ample facilities to hold a conference. Sydney's population is 4.5M vs 4M for Melbourne.