The cost of setting up the Auckland Super City has risen to $112 million after a blowout in costs incurred by the agency merging the eight existing councils into one.

The Government provided an additional $36.9 million in last week's Budget to the Auckland Transition Agency to provide critical services for the Auckland Council to be up and running on November 1.

The agency initially set a budget of $34.4 million for the period up until October 31, but has previously not publicly disclosed its implementation costs, such as information technology and systems to separate transport functions into a mega-council controlled organisation.

The $71.3 million loan from the Crown to the agency must be repaid by Auckland ratepayers by November next year.

On top of of the agency's soaring bill, the cost of setting up a mega-water company is $26.5 million and the region's existing councils have spent or budgeted a further $14.2 million.

The councils' costs and setting up Watercare Services have been funded out of current budgets.

Local Government Minister Rodney Hide gave no inkling of the cost blowout by the agency in an Official Information Act response on "the costs of setting up the new Auckland Council" to the Herald on April 21.

He said the Royal Commission on Auckland Governance estimated a set-up cost of $120 million to $240 million and his goal was to bring it under that budget "and we will".

Mr Hide said that when the Government looked at the long-term plans of the existing councils, it took out a lot of spending on things such as information technology.

The Labour Party's spokesman on Auckland issues, Phil Twyford, said it was an extraordinary doubling of the agency's budget.

"The Government has not told Aucklanders how much the transition will cost and what impact it will have on rates."