The commission of investigation into the Mother and Baby homes has cost €3.73 million to date.
The commission, which was established in February 2015, is tasked with investigating allegations of abuse at 14 institutions and four county homes between 1922 and 1998.
Figures released to The Irish Times show the costs of the inquiry, which is chaired by Judge Yvonne Murphy, were €1,485,676 in 2015 and will reach a further €2 million this year.
The majority of the monies has been spent on pay, with salary costs reaching €1.7 million over past two years.
Operational costs formed a significant part of the commission’s budget, reaching €414,628 this year and €267,357.
A confidential committee, which meets survivor groups and those who worked in the homes, has been shaping the commission’s work.
Agreement was reached in late 2015 that expenses would be provided to witnesses who gave evidence to the committee.
The bill for payments to more than 150 such witnesses was €23,404 in 2015 and €67,864 this year.
That is expected to rise in 2017 with meetings of the confidential committee due to take place in a number of locations in the United Kingdom.
In addition the Department of Children has incurred costs of €400,000 for its role in assisting the commission.
The commission, which was established by the former minister for children James Reilly, was due to report back earlier this year.
However, it was granted an extension by the Government and will now not present its findings to the Government until February 2018.
Three individual reports will be delivered to the Minister for Children Katherine Zappone.
Only 14 institutions and four county homes across the country fall within the commission’s terms of reference.
The terms include an investigation into high mortality rates recorded in these institutions, the living conditions and social care arrangements in the homes and the exit arrangements made for single women and children on leaving.
The commission will have the power to investigate alleged forced and illegal adoptions from the homes and the relationships between the institutions and children’s homes, orphanages and adoption societies.
It will also investigate postmortem practices including the reporting of deaths, burial arrangements and the transfer of remains to educational institutions for anatomical examinations.
A spokesman for the Department said: “The Commission was established by Government on the 17th February 2015 and has offices on lower Baggot Street, Dublin 4.
"The costs associated with this Commission are met from the Vote of the Department of Children and Youth Affairs.
“Since its establishment in 2015 the Commission has incurred costs of approximately €3.326 million (to mid-December 2016).
“It is anticipated that the Commission’s total expenditure for 2016 will be in the region of €2 million.
“In addition, the Department has also incurred additional costs of approximately €0.405 million to date in supporting the establishment and operation of the Commission.”
The terms of reference of the inquiry have been criticised strongly by those representing the survivors of the mother and baby homes.
They believe the commission should extend its scope and report back within an earlier timeframe.