ON1407
Just saw this from internet, Book 5 or More Days, Get 2 Days Free (Book 5, Pay for 3).
I'm going to be away for 4 days not sure if I could pay for 5 days and get 2 days free, will ask tomorrow.
But sounds a good deal.
Their normal rates are quite competitive too:
http://www.andrewsairportpark.com.au/adelaide/rates.aspx