It costs the taxpayer £81,340 annually to house a prisoner in Northern Ireland, according to a prison service report released on Thursday.
The figure is up slightly from last year (£81,254), but down by over £4,000 from 2004/05 (£85,935).
The report also revealed the prison service's participation in the Billy Wright Inquiry cost over £1.1m in the last year alone.
The loyalist leader was shot dead in the Maze Prison in 1997.
Meanwhile, the current rate of absenteeism among prison service staff is 14.5 days, according the report.
This compares to a figure of 17.7 days for the previous year.
Fifty-seven per cent of staff had no sick absence during the year, while 84% of sick absence was accumulated by 16.5% of staff.
Commenting on the overall report, Prisons' Minister Paul Goggins said: "The Northern Ireland Prison Service has faced a difficult year, particularly following the death of inmate Colin Bell on 1 August.
"This tragic incident has already had significant consequences. The recommendations included in the Pearson Report and the increased emphasis on safer custody will continue to have an impact on the working environment."
Colin Bell, 34, who was serving a life sentence at Maghaberry Prison for murder, hanged himself at the fourth attempt.
He was on suicide watch and was meant to be monitored every 15 minutes.
It is understood that video camera footage examined as part of the surrounding investigation showed prison staff lying in bed watching television while they were supposed to be on duty.
Mr Goggins continued: "The new Sentencing Framework will mean a large increase in the number of prisoners subject to licence conditions on release.
"The prison service will face additional challenges in the year ahead as it becomes a more modern and accountable organisation that is able to deliver effectively on the key areas of public protection, safer custody and resettlement."