The inquiry into the handling of the so-called 'Grace case' is set to cost the State €7.5m.
A senior barrister has been given 12 months to examine how a profoundly disabled woman was left in an allegedly abusive foster home.
The inquiry will then investigate the treatment of 47 other people who were resident in the same home.
The inquiry itself will cost €5 million, with a further €2.5m set aside for third party legal costs.