Council property services group manager David Bainbridge was asked about the cost this week, after it was confirmed last week the council had budgeted $2million to fix the building.
In June, council staff estimated the repairs would cost less than $1million.
Mr Bainbridge said this week the June estimate had been "very rough" and based on an earlier consultants' report on the state of the building.
"As we've progressed with planning and design, the scope of the work required and likely costs have become clearer."
The $2million budget also included a contingency, "and the actual costs may not be that high", he said.
"We still don't have a final design and the costs will be confirmed in the coming months.
"Input from geotechnical engineers and some further analysis of previous reports are needed to complete this stage - these are expected soon."
The council hoped to apply for building consent once a detailed design was ready, and expected to start building work early next year, in consultation with Edgar Centre staff, he said.
Earlier this year, it was reported two consultants' reports, prepared for the council in 2016 and 2017, had found the venue's three main buildings were all significantly earthquake-prone, at 10%-15% of new building standard (NBS).
The entire complex was also being affected by subsidence, which was warping floors and creating other headaches, including leaks and other weather-tightness issues, the reports showed.
Despite that, the council has decided the sports complex - which caters to 650,000 people a year - would remain open until repairs were carried out.
Mr Bainbridge said the work would bring the building above 34% of NBS, meaning it was no longer considered earthquake-prone.
No decision had yet been made on whether to pursue compensation through the courts.
"We're focusing on resolving issues with the building first and it's too early to make any decisions about our legal options," he said.
