Whangārei is at risk of losing a huge government grant for a conference and events centre, plaza, bridge and ferry terminal.
Last year the Provincial Growth Fund committed $60 million to the Ōruku Landing plans for the city's waterfront.
But the district council needs to pledge $70 million this month, or the project will collapse.
If Ōruku Landing goes ahead, private developers say they will build a neighbouring 4-star hotel, apartments and a car parking building.
Northland Chamber of Commerce chief executive Steve Smith called the project a "very rare" opportunity.
When public consultation started last month, the council said the development would cost $123 million.
But two weeks ago, the council got a new report, suggesting costs would likely be $13 million more.
That would mean a 7 percent rates rise.
Project supporters say that isn't much, equating to the cost of one takeaway coffee a week for most residential households in Whangārei.
District councillor Simon Reid (Ngāpuhi) told RNZ a massive amount of groundwork had already gone into the project, and public consultation - that ends tomorrow - was just one part of it.
"The staff collate everything, they will bring them to us [elected members] at council and then we can start making decisions from there on. It has been quite a process so far and it's by no means finished."
Whangārei MP Dr Emily Henderson hoped the majority of submissions would back the project.
She saw big financial benefits for the city, from the construction phase, through to spenders using the facilities.
"I think that this is a chance worth grabbing and I would be sad to see Whangārei's community lose out on this money."
National's deputy leader Dr Shane Reti (Ngāpuhi, Ngāti Wai, Ngāti Hine, Ngāti Kura), who is Whangārei-based, didn't think residents understood the proposals enough before consultation began.
"I've been hearing concerns for the increase in rates that will come with it. I've been hearing concerns for the business case - to make sure that it doesn't continue to be a drawdown on ratepayer funds. But on the other hand, I've also heard of the opportunity that should be grasped."
Whangārei kaumātua Millan Ruka (Te Uri Roroi, Te Māhurehure, Te Parawhau) who has spent his life working in construction and conservation, is one resident strongly opposed to the plans.
He said he is "not against private enterprise" but he is uncomfortable with the fact the feasibility projections changed halfway through the public consultation process after many people had already made submissions.
"It's just not professional," he said.
"As a builder, I would not step forward, it's just not tidy enough."
Whangārei district councillors will meet next week to decide the project's fate.