Senior civil servants who selected the new Mountjoy prison site were told not to take the cost of potential locations into account, after they had difficulties finding a suitable location from their shortlist.
It emerged that five sites previously excluded as being too expensive were reintroduced after the civil servants changed the criteria of selection to exclude cost, following a direction from the Irish Prison Service.
Details of the lifting of the cap come as the Government has been criticised by Opposition parties for paying too much for the final site, Thornton Hall in Meath, a 150-acre farm four miles south of Ashbourne near the N2 and a proposed interchange for the M2 motorway. It was zoned as agricultural land.
The Government paid €29.9 million, or just under €200,000 an acre, which it argued was good value compared with other sites it was considering.
This compares with an average price for farm land in rural Dublin of €17,152, according to a recent survey by Ganly Walters.
Land zoned for residential property would expect to fetch in the region of €200,000 plus in north Co Dublin, while commercially zoned land could expect to fetch €120,000- €200,000, according to property experts.
It has also emerged that impact on the community and accessibility to public transport were ranked as less important than the shape and size of the site and the availability of services.
According to the minutes of the Mountjoy Complex Replacement Site Committee, Thornton Hall was only considered as a last-minute option after a deal on another site fell through.
The committee began in early July to consider 31 sites in Wicklow, Meath and Kildare, all within 20 miles of Dublin. They were ranked on eight criteria - cost; general location; proximity to public transport; availability of emergency services; access; shape/size of site; availability of services, and impact on the community.
Six sites, at Finglas, Baldonnel, Leixlip, Bullstown, Corrstown and Kilcock, were selected for a second stage, with more information sought on an additional seven sites. Two of those seven, at Clonee and Dunboyne, were selected for stage two. Baldonnel and Dunboyne were then eliminated.
At the end of August it emerged that the favoured site, at Finglas, was no longer for sale, while sites at Bullstown and Corrstown were also dropped, leaving just three, all with problems, including distance from Dublin.
The following month, the committee was advised that the director general of the Irish Prison Service requested that sites previously excluded on cost grounds should be re-evaluated.
The committee, made up of senior civil servants from the Prison Service, the Department of Justice and the Office of Public Works, then removed the cost evaluation criterion and gave a higher rating for the site.
Property agents for the Government began detailed negotiations on three sites, two of which had been previously excluded on cost grounds - Coolquoy, a few miles south of Ashbourne, and Sillogue, near Ballymun. Sillogue scored highest on the selection criteria.
By the end of November, Coolquoy emerged as the favourite, after the owner of the Clonee site "had not been open to realistic discussions and the cost of the Sillogue site had escalated to circa €500,000 per acre", according to the minutes. Discussions began on Coolquoy, with a price of €31.35 million agreed by early January, down from an original asking price of €40 million. The site owner then pulled out of the sale.
The Government's property agent, Mr Ronan Webster, then informed the committee of Thornton Hall, a new site close to Coolquoy, which was eventually selected. In terms of the selection criteria, it scored nearly 95 per cent on the shape and size criteria, but just 55 per cent in terms of impact on community and 50 per cent in terms of general location.