Close to €1bn has been spent on purchasing homes from the private housing sector since 2011.
The average cost of a unit purchased was €162,000, rising to €221,000 in Dublin.
According to the Department of Housing’s figures, it would have cost €22,000 less (€199,000) to have built an entirely new unit in Dublin during the same period.
In Cork, the average price paid for a unit was €191,000 but building a new home would have saved €36,000, costing a total €155,000.
Ireland’s local authorities have built just 2,354 new units since 2011.
The figures were received by Fianna Fáil through Freedom of Information requests made to each of the 31 local authorities.
"This data has revealed that Government has spent just short of €1bn in tax payer’s money to purchase 5,559 homes, pricing families trying to buy their own homes out of the market without adding to the national stock," said Fianna Fáil housing spokesperson, Darragh O’Brien.
“Not only has the FG plan driven up house prices generally but in many instances it would have been significantly cheaper for the State to build new social homes.
“This sad narrative is the very same in every county up and down the country; no vision whatsoever to bring new housing stock on stream and a severe overreliance on the private sector.
“Affordable housing needs to be at the core of the forthcoming Budget and we will fight hard to force FG towards adopting a Comprehensive Affordable Housing Scheme."