The cost of the report into Mayor Len Brown's extramarital affair with Bevan Chuang has reportedly risen to $250,000.
The Auckland Council is refusing to confirm the figure, but a source has told the Herald that the $250,000 figure is correct.
Former council chief executive Doug McKay said in December the EY (Ernst & Young) report and associated costs would exceed $100,000.
It is understood new chief executive Stephen Town briefed a committee of five counsellors who are negotiating a settlement with Mr Brown towards the bill, about the full costs last week.
Expectations are rising for the settlement by Mr Brown to be made public. Three of the five councillors believe it is the wish of the group to make the settlement public.
Mr Brown has told the Herald he would abide by the wishes of councillors.
Taxpayers' Union executive director Jordan Williams questioned how the original budget of $75,000 has turned into a $250,000 cost blow out.
Mr Jordan said the union understood it was Mr Brown's lack of co-operation and dependence on lawyers that caused the costs to escalate.
As well as EY, the council sought legal advice from Crown Solicitor Simon Moore, QC, and may have to pay some costs to the Auditor-General, who was involved in the process.
A council spokesman said councillors' discussion were ongoing and it would be inappropriate to comment at this stage.