Here is a new site for price checks on Pinball Machines at the moment more for the US but you can still use it as a guide and add $500 to $1000 for most machines to match Aussie prices.
Ensure when you check a machine to select the search option and found to be a little fussy in searching so for
Iron Man just write
Iron and then a list will come up
http://www.pinballprice.com/index.htmlmaybe Nino or Nick can sticky this to the top as a resource with Pinpedia