The Irish Prison Service has reported a slight fall in the cost of keeping a person in jail due to stricter overtime budgets and the closure of prisons at the Curragh and Spike Island.
In its annual report for last year, the service said the average cost of keeping an offender in custody was just under €84,000-a-year, down around €4,000 on the figure for 2003.
Portlaoise Prison was identified as the most expensive, costing up to €250,000-a-year for each inmate.
Elsewhere, the Prison Service said the number of people sent to jail in 2004 was 10% lower than in 2003, mainly due to a fall in the numbers detained under immigration law.
However, the average number of people in custody on any one day was 3,199, up 1% on the figures for 2003.
It cost around €80m to hold immigrants before they were deported in 2004, while the prison overtime bill was €45m, down €20m on the previous year.