The State Government's plan to amalgamate metropolitan councils will cost nearly $100 million in one region alone, a report says.
The first detailed economic analysis of local government reform to be released, the report estimated the carve-up of the south-west metropolitan area would cost $97.8 million.
The Government proposes to create 10 merged councils and adjust the boundaries of two others.
In the south-west corridor, Cockburn will be split between the cities of Fremantle, Kwinana and Melville.
The paper, commissioned by a Cockburn community group and conducted by economic consultants AEC Group, found that splitting an existing local government made mergers complex and significantly more costly.
The Cockburn Community Steering Group has submitted an alternative proposal for reform costed at just $24.3 million. It has Cockburn merge with Kwinana as a whole and Fremantle amalgamate with East Fremantle.
Cockburn steering group representative Geoffrey Sach said the Government's rationale was to make councils more sustainable but economic modelling showed only the City of Melville would benefit.
"Melville, which is already the second-most sustainable council in WA, would become richer and the rest of us get poorer - go figure," he said.
Mr Sach said one rationale for splitting Cockburn was to make Fremantle more sustainable but the economic analysis indicated the opposite.
"Fremantle will get a portion of Cockburn, which would increase income 43 per cent, but asset liability would go up 76 per cent - making Fremantle even less sustainable," he said. "It's like saying, I'm giving you all this old stuff to look after but I am not giving you enough money to do it."
The report also identified there could be a $100 million economic shock in the regional economy because of planning and building approval delays and a loss of up to 800 jobs caused by the carve-up.
Local Government Minister Tony Simpson said his department had commissioned its own economic analysis of the changes, which was part of a confidential Cabinet submission.
Asked how much metropolitan reform would cost, Mr Simpson said it would be irresponsible to "bandy figures around".