The pedestrian causeway - believed to date to the 1850s - was described as a find of national significance when discovered during excavations for the Wall Street shopping mall in May 2008.
About 60% was too rotten to save, but the rest has remained in a chemical bath since then while being slowly prepared for drying and display inside the mall and the refurbished Toitu Otago Settlers Museum.
Council city property manager Robert Clark said the bill for the work to protect the remnants now stood at $106,335, and was likely to rise.
Almost all of the spending had gone on the work of wet-wood conservation expert Dilys Johns, of the University of Auckland.
Her work had so far cost the council $99,000, which included her fee, flights to and from Dunedin, accommodation if needed, reports and other costs, Mr Clark said.
Mr Clark believed her work had been carried out "reasonably efficiently", and the rest of the council's bill covered equipment hire and drying racks.
It was likely the bill would increase when some of the material was put on permanent display under a glass floor inside the mall, but costs were still being investigated and yet to be confirmed, he said.
"It won't be in that sort of league," he said.
The spending was authorised by councillors at a full council meeting in August 2008. The meeting approved a budget of up to $310,000 to cover the cost of off-site preservation, reinstatement and display of the causeway's remains, Mr Clark said.
Councillors voted 12-3 in favour of the resolution, with deputy mayor Chris Staynes, Crs Kate Wilson and the late Richard Walls opposed.
Staff were also asked to report to the council's property subcommittee if that budget was to be exceeded, which had not happened.
After a long wait, it was finally confirmed last month parts of the remaining causeway were expected to be ready for display by next month, and the rest by early next year.
Mr Clark defended the cost, saying he also felt "reasonably strongly" the causeway was worth saving.
"It is a historic part of Dunedin"
