Trafford Council this week estimated it would save around pound;250,000 annually if its seven grammar schools were axed.
The Labour-controlled borough said the savings would come from the cost of test material and officer time.
Chris Pratt, assistant director, said: "We have not done a detailed analysis, but we have done some rough work which shows savings in the region of pound;250,000 a year."
The figures were revealed as the propaganda war over the 166 remaining grammar schools gathered pace. Last week the Conservatives claimed the national bill for abolition will be pound;500 million - figures taken from estimates in Tory-controlled Kent, which runs a fifth of the country's grammar schools. Kent says that scrapping the 33 schools could cost as much as pound;150m.
"This has major implications for the entire secondary education system," said the Conservative education spokesman, David Willetts.
The pound;500m, he said, would have to be found from already stretched council budgets. Kent's estimate is based on the capital cost of reorganising the county's education system - the price of new buildings or amalgamating schools.
An internal council document warns that the implications of change would be very significant, and adds: "The cost of change would be substantial but is currently unquantifiable. Costs might be offset by presently unquantifiable savings."
Officials looked at options including:
* changing the status of all schools to comprehensive;
* amalgamating schools where possible to create schools of at least six forms of entry (900 pupils), keeping split sites;
* amalgamating schools to ensure all had a minimum six forms of entry on a single site;
* the previous option - even if that required acquiring new sites and total rebuilding.
But the officials costed only this last, most expensive option.
Martin Frey, from STEP (Stop The Eleven-Plus), the campaign group for Kent and the Medway towns, accused the council of scaremongering. He claimed the annual cost of administering selection in the county was pound;4m, and said savings could also be made if children did not have to be bussed all over Kent.
Joanna Wainwright, Kent's head of education policy, said the only budget the county had for selection was pound;139,000 spent annually on test materials.
WHERE THE BATTLE GOES ON
Authorities with grammar schools (numbers in brackets): Barnet (3), Bexley (4), Birmingham (8), Bournemouth (2), Bristol (2), Bromley (2), Buckinghamshire (13), Calderdale (2), Cumbria (1), Devon (1), Enfield (1), Essex (4), Gloucestershire (7), Kent (33), Kingston upon Thames (2), Kirklees (1), Lancashire (4), Lincolnshire (15), Liverpool (1), Medway (6), North Yorkshire (3), Plymouth (3), Poole (2), Reading (2), Redbridge (2), Slough (4), Southend (4), Stoke-on-Trent (1), Surrey (1), Sutton (4), Torbay (3), Trafford (7), Walsall (2), Warwickshire (5), Wiltshire (2), Wirral (6), Wolverhampton (1), The Wrekin (2).