A council spokesman said the total moving cost included a $46.7m refurbishment, and was given the green light because it was the cheapest option long term.
Existing leases were due to expire and moving staff from seven buildings into three would save more than $100m over the next 20 years.
"Re-fit money was all in the council's current corporate accommodation renewal budgets — a big chunk of it was designated for the civic administration building in Greys Ave ... The only new money was for the acquisition of the building," he said.
A spokesman for Brown said no money had been approved or spent on the tower's new mayoral office, but $86,000 had been spent on refurbishing Brown's existing Town Hall mayoral office in the last four years. "That work was approved and carried out well before the council's decision to move to [the former ASB Tower]."
Brewer said ratepayers would be "infuriated" by the move and that the mayoral office's planned new home could never compare to the Town Hall.
"It's a very special place and the likes of international visitors love its gravitas." Brown's spokesman said the Town Hall would still be used to host visitors, ceremonial events and council meetings.
It is not the first time the office of the mayor has moved — former Auckland City mayor John Banks spent $8,463 in 2001 to switch from the 15th floor of the Civic Building to the Town Hall.
Banks claimed at the time he would pay for that over his mayoral term by cutting the alcohol budget for his office to zero. Once Brown, his staff and councillors move out, the Town Hall will host the Waitemata Local Board and its staff. No alterations or refurbishments are planned, and moving costs will be part of the overall council budget for the shift.