Costs have been split among the region's councils with Hamilton City Council committing $276,000 so far.
But city councillor Martin Gallagher this week revealed spatial plan costs could balloon to more than $1 millon and questioned how much new information would be contained in the document.
The spatial plan aims to look at where the region is at, and analyses information in the context of where the region wants to head, long-term.
The draft plan will be delivered in December next year.
Gallagher said the spatial plan would give the region "one voice", but he hoped it did not reinvent information already known.
"The $1m in the end is for a report, there's no community centre that comes out of it, there's no piece of tarseal," he said. "There's an issue of one voice for the Waikato, and yet the plan doesn't appear to address the issue of governance."
Waikato District Mayor Allan Sanson, who chairs the mayoral forum, said the spatial plan's budget was drawn up two years ago but did not include engagement or communication costs.
The new costs were expected to be finalised in mid-January, but Sanson said it was unlikely the joint committee, working on the plan, would endorse the $1m-plus price tag.
"We realise we can't do this plan without engaging special interest groups, industry and iwi and that comes at a cost," he said.
"Engaging with iwi comes at a cost and also takes a lot of time. But the figure is a bit high and the joint committee will look at how much lower it can come down."
Sanson said he appreciated Gallagher's concerns, but believed the spatial plan would generate benefits for the region and help Waikato tap into government funding. Currently, central and local government invest about $8 billion a year in the Waikato.
"It is a lot of money but a lot of work is going into this document and it will help us map out the future of our region. It will help identify future growth, where there are opportunities and will help us work alongside industry to give them a steer forward."
The spatial plan will draw on information from council documents, census data and advice from the National Institute of Demographic and Economic Analysis.
The spatial plan joint committee includes staff from partner councils, non-local government members and Latitude Planning Services director James Bevan.
He told the Waikato Times he could not comment on the plan because his terms of reference prevented him from talking to the media.
The joint committee is chaired by Margaret Devlin, and will meet again on February 9.
Sanson said the region had achieved strong results when it spoke with a united voice, such as when it secured $2.4 billion funding for the Waikato Expressway.
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