The government argued the detention centre was required to deal with sick asylum seekers and refugees on Nauru and Manus Island who were approved for medical transfer under legislation passed earlier this year with Labor and the crossbench’s support.
Mr Morrison had also accused the opposition of encouraging people smugglers to restart their trade by supporting the legislation.
But the budget revealed that the government intends to repeal the medevac legislation if it wins the May election and then re-close the centre by July.
The Treasurer delivers the 2019 Budget
The facility, which has the capacity to house 250 people, remains empty.
No asylum seekers or refugees have been transferred to Christmas Island from Manus Island or Nauru since the medevac legislation passed in February.
Finance Minister Mathias Cormann defended the prime minister’s previous $1 billion cost estimate, saying the figure was based on advice from intelligence agencies at the time.
Senator Cormann said the government would reverse the “reckless” legislation to limit the number of asylum seekers accessing a medical transfer.
Mr Morrison toured the newly re-opened detention centre in March accompanied by a media contingent to show Australians it was "up to the job".
The trip was criticised by the Opposition as an expensive "waste of time".
An extra $58.6 million has been set aside for ASIO next financial year to boost border security.