The Public Accounts Committee has estimated that the cost to the State of the three tribunals of inquiry could be as much as €366m.
That estimate is based on the pattern of costs experienced to date.
The Mahon Tribunal, which is investigating certain planning and payment matters, has so far cost the State €105m.
The Moriarty Tribunal which is examining payments to politicians and the awarding of the second mobile phone licence cost the State more than €41m up to the end of last year.
The cost of the Morris Tribunal at the end 2010 was just less than €58m.
PAC says five senior councils have been paid more than €5m for their work on the tribunals.