The Turnbull government’s controversial GST deal with Western Australia will cost federal taxpayers $52.9 billion over 10 years, which is $44 billion more than originally promised, the federal budget says.

The deal, which neither side of politics dares tamper with for fear of losing seats in the west, will result in the Commonwealth having to pay the other states GST top-up payments worth $52.9 billion between 2019-20 and 2029-30.