The cost of Parliament's dual citizenship imbroglio has been laid bare in the Turnbull government's mid-year budget update.

Taxpayers will fork out $11.6 million in the 2017-18 financial year for legal costs arising from the saga, which has dragged on for nearly half a year and seen a slew of MPs appear before the High Court.

Some of Australia's top silks were enlisted to battle it out in the landmark 'citizenship seven' case, which ended with five MPs including Deputy Prime Minister Barnaby Joyce, deputy Nationals leader Fiona Nash and One Nation senator Malcolm Roberts being thrown out of Parliament.

Mr Joyce was represented by leading barrister Bret Walker SC. Former solicitor-general Justin Gleeson SC and former Federal Court judge Ron Merkel QC represented Mr Joyce's challenger at the 2016 election, Tony Windsor, who argued for the Nationals leader's elimination.