House Sales Data
Depending on what state you live in your state govenment should provide online facilities for you to determine the vaul of properties sold in a particular area.
The land titling records of the State of New South Wales provides information on NSW historical Private house sales ( or any recorded sale) which you can access by using the Lot and plan number ( ie Lot 23 DP789678) current cost is 10.75
http://www.lands.nsw.gov.au/
In QLD you can access this information at the Dept of Natural Resources and Water Valuation and sales data products are available for all of Queensland.