The upfront cost of merging Welsh councils could range between £160m and £268m.
That's according to the Chartered Institute of Public Finance and Accountancy (CIPFA)
But it also says this is offset against potential savings of £65m a year across all councils after a three year period.
In the study CIPFA Wales evaluated a number of areas where the costs of transition and recurrent savings are likely to be significant.
These included people change costs, including redundancy, of up to £158m; property, systems and other change management costs of around £54m and income forgone because of council tax harmonisation of at least £57m.
Councillors in Cardiff faced a noisy demonstration this afternoon as they met to decide on cuts to jobs and services in the city.
The council is facing an unprecedented £50m budget deficit which will mean having to cut some 600 jobs.
Richard Morgan reports.
Angelsey County Council has agreed a council tax rise of 4.5%, after discussions over next year's budget.
Monmouthshire council will meet today to decide how they can make cuts to their budget.
Ideas suggested by councillors so far include dimming some street lights and raising the cost of school meals.
The authority needs to save £9m in its budget for the next financial year and £20m over the next four years.
The council asked members of the public for their ideas last year and said it was looking seriously at some of them.
These included setting up a lottery, which could raise money for specific projects, increasing the price of school meals and reducing street sweepers.
Councils across Wales are currently reviewing services in response to a reduction in their budgets from the Welsh government.
Wales' biggest council will meet today to decide how millions of pounds of savings will be made to its budget.
Last week, Cardiff council's cabinet approved a report which looked to save almost £50m from its budget for the coming financial year.
The report includes proposals which would cut the equivalent of around 600 jobs and raise council tax by nearly 4%.
The council may face cuts of around £120m over the next three years.
Earlier this week, Powys County Council postponed their decision until March.
Caerphilly County Councillors have approved a series of budget proposals for the forthcoming year at a council meeting this evening, which will see savings across the council for 2014/15 in excess of £14.2 million pounds.
Councillors also approved plans for a 3.9% increase in Council Tax, which in monetary terms equates to a 69 pence per week increase for a Band D property in Caerphilly county borough.
Members also supported plans to further increase the Living Wage by an additional 20 pence per hour, which will ensure that thousands of the council?s lowest paid staff earn at least £7.65 an hour, an increase of 20 pence from £7.45 as currently.
A report into the way public services are run here in Wales is expected to recommend a radical reduction in the number of local councils. The Williams Commission was appointed by the Welsh Government to look at the way services are organised and to suggest ways of improving their efficiency.
It's widely expected to say that Wales has too many local authorities and that rather than 22 separate councils there should be far fewer. Some reports suggest it will recommend halving that number through mergers instead of drawing up new boundaries.
Councils have warned that reorganisation will be difficult, expensive and could lead to thousands of job losses.
Welsh local authorities are under growing pressure to save money, but they still have greater freedom to raise council tax than in England.
One London borough has gone further, cutting tax by 17 percent since 2006.
Owain Phillips reports.
Welsh Councils are being warned of a bleak financial climate, with deep spending cuts lasting until 2021. A report to be launched a Welsh Local Government Conference later today says public services in Wales face a hugely challenging future following spending cuts and reforms to the welfare system.
It claims that three-quarters of public spending cuts are yet to come and that although there'll be some protection for the most important services, the unprotected ones could be cut by 52%. The report was commissioned by the Welsh Local Government Association, the WLGA.