Planning fallacy
The Sydney Opera House was expected to be completed in 1963. A scaled-down version opened in 1973, a decade later. The original cost was estimated at $7 million, but its delayed completion led to a cost of $102 million.
Point Piper, New South Wales
John Symond's mansion on Wingadal Place, reportedly cost over 70 million to build (excluding land), easily making it Australia's most expensive, privately owned residential home. In 2007, "Altona", located in Wunulla Road and Australia's second-most expensive house, was listed for more than $50 million. It was sold in 2013 for a price thought to be more than $50 million, which was a Sydney record.