A single council for the Bay could save up to $10m a year but the move to merge Wairoa, Napier, Hastings, CHB and Hawke's Bay regional councils could cost $18.4m.
The proposal, by A Better Hawke's Bay, would also mean up to 100 public servant jobs will be cut if the five councils were merged.
The figures were released in the second and final part of the Hawke's Bay region Prosperity Study by consultants McGredy Winder & Co. The report was tasked to refine cost and saving estimates associated with local government reform options, after the scrutiny of figures identified in the first report released in August 2012.
The report reviewed three scenarios including the A Better Hawke's Bay plan for a single council, a second scenario for a single territorial council and the existing regional council and a third for two territorial councils north and south of the region as well as the existing regional council.
The report said between 90 and 100 jobs would be reduced under the A Better Hawke's Bay Plan. The second scenario would involve jobs cuts of between 70 and 80 while the third, 30 to 40 jobs.
"The breakdown of potential savings by activity has not been reported here in order to avoid unnecessary uncertainty and speculation by staff within each activity of council operations," the report said.
A Better Hawke's Bay's proposal had the highest transitional costs but also the highest potential savings compared with the other two scenarios.
A Better Hawke's Bay chairman Rebecca Turner said the transitional costs to move to one council would be recovered inside two years through $10m annual savings made by having a single local government authority.
"It is also vitally important to not forget that the financial benefits are only part of the advantages flowing from local government reorganisation.
"The first stage of the Winder Report highlighted the other benefits coming from unified regional leadership, a regional vision and the simplification and consistency of policies for business and the community. This along with the improved capacity to influence the effectiveness of the flow of the more than $1b of central government funding that comes into the Hawke's Bay region each year."
The Winder report relied heavily on information from the Auckland super council merger.
"Moving to a common rating system across Auckland resulted in substantial shifts of the rating burden between different geographic areas of the city.
"The impact of this sort of change is likely to be far larger for ratepayers than the size of potential savings identified in this report."
The report would be presented to the HBRC on June 26.