Council staff told councillors there were "cost pressures" with the project, but had been told to continue investigating it.
"At this stage we are still looking at $5-6 million."
Mrs Chadwick said more money could potentially be allocated from within the Long-term Plan "funding envelope" to the project but that would not result in a rates increase or extra debt.
"To get excited at this stage and say it is an added impost to the ratepayer is far too early, too premature and a little bit excitable."
Mrs Chadwick said as long as the financial decision made at the end was within the Long-term Plan she was "perfectly happy for it to proceed and continue".
Council chief executive Geoff Williams said the original $5 to $6 million was an "estimate" and more detailed information allowed for more accurate costings.
The project is about to go to a detailed design stage which would include quantity surveyor costings and they would then go through a "value management approach" where savings could be made or items cut.
He said there would be no final costs until the project got to contract and it was only then they would know if it would need more than budgeted for.
"I've indicated there are certainly cost pressures in this project, the clear direction that I have got back is to continue to look at investigation of the project, to look at its affordability but to do so with the clear expectation that this will not come at the cost to the ratepayer in terms of a rate increase nor increased debt outside of our [plan] framework."
Councillor and chairwoman of the Rotorua District Residents and Ratepayers group Glenys Searancke said the public was entitled to know what the project would cost before it was too late to turn back.
"We believe the public has a right to know the estimated cost overruns now.
"We are talking about a lot of money. Then we can ask the question if we should be going ahead with the project at all."
The business case signed off by the Government gave the Lakes District Health Board a budget of just under $4 million, its communications officer Sue Wilkie said.
Miss Wilkie said the health board had no intention of allocating extra funding to the project on top of that.
"Part of the current way forward is to adjust the designs in line with what is affordable for both the Rotorua Lakes Council and the DHB."
Additional reporting
Matthew Martin