expired $695 for Bosch Ultma 880 3 Sensors Home Security System Fully Installed
Cheapest I have found and seems they have 10 years history in Melbourne.
Edit: Thanks Maz78 - Apparently http://www.ebay.com.au/itm/Home-security-system-fully-instal... only $520.
Edit: nd here http://www.ebay.com.au/itm/Bosch-Alarm-FULLY-INSTALLED-490-/... $490.
Looks like there are cheaper deals if you look around.