The Department of Corrections invoked a "stepping in" clause in Serco's contract in July amid concerns of organised violence and injuries to prisoners at the jail.
Corrections Minister Judith Collins said today the total cost of this action, combined with outstanding performance notices, was $8 million.
She also confirmed that the Corrections Department would continue to manage the prison until the end of Serco's contract in March 2017.
The British-based company would only provide staff at the jail, Mrs Collins said, and would make no profit during this period.
"This is a pleasing outcome as it both recovers costs and gives more certainty over the future management of the prison," she said.
Corrections chief Ray Smith decided to return the Mt Eden prison into his department's control in response to high rates of violence and drug use among inmates.
Serco received several performance notices for these incidents, which meant it was unable to get its full performance-related bonus.
In December, Mr Smith confirmed that Serco's contract to run the prison would not be renewed at a break point in March 2017.
Ms Collins said Corrections would continue to manage the prison after Serco's contract ended, and a longer-term plan for the prison would be determined at a later date.
