It was initially forecast 500 units would cost €100 million in total - or €200,000 each - according to a report by the Comptroller and Auditor General.
However, the State's auditor now projects the number of homes has increased to 654 and will cost a total of €285 million - or around €436,000 per unit.
Around 87% of the units have been fully completed as of last month, with the full roll-out expected before April of next year.
