The detention centre on Manus Island has cost Australian taxpayers about $2 billion since it was reopened four years ago – more than $1 million for each of the 2000 people who have been imprisoned there.

As the Turnbull government scrambles to find a place to send the 854 refugees and asylum seekers that remain in the notoriously harsh facility after it was declared illegal by Papua New Guinea's Supreme Court, a new analysis reveals just how much it has cost the federal budget to build and run the centre.

Parliamentary Library analysts have trawled through years of Senate estimates hearing transcripts to piece together a total cost for Manus Island. Credit:Jason South

While official figures relating to the cost of offshore detention are opaque, analysts in the Parliamentary Library have trawled years of Senate estimates hearing transcripts to piece together a total cost for Manus.

They show the centre has cost Australians at least $420 million to build and maintain, and $1.25 billion to run since the Gillard government reopened it in late 2012 – giving a total of more than $1.6 billion.