The cost of running Australia's network of onshore immigration detention centres has fallen by more than $1 billion a year.
There are now 1550 people in immigration detention on the mainland, down from a record 10,200 in 2013.
More than 70 per cent of detainees have committed crimes and will be deported as a result.
Taxpayers shelled out $649 million on running immigration centres in the last financial year.
This was down from $1.89 billion in 2013/14.
Acting Immigration Minister Alan Tudge put the saving down to strong border security, and could not resist dropping his boot into Labor in the process.
The departmental figure does not include the cost of running offshore processing in Papua New Guinea and Nauru.
There are still roughly 180 refugees and asylum seekers in PNG, and about the same number in Nauru.
The United States has agreed to take up to 1200 refugees from Australia's offshore detention centres.
There have been 785 people resettled in the US under the deal, including 140 so far this year.
Transfers have continued throughout the coronavirus pandemic despite disruptions to global travel, with more departures scheduled within weeks.