There's some details here: http://eftm.com.au/2016/08/census-2016-the-10-million-online...

"The ABS paid an Aussie company “Revolution IT Pty Ltd” $469,367.50 across three tenders to undertake “Load Testing Services for Census 2016”. $325,000 of that was for software licences to get the equipment required to do the testing, the rest we can assume was for the teams to actually undertake the testing."

And hosting is being provided by IBM: http://www.itnews.com.au/news/ibm-wins-96m-to-host-ecensus-i...