Electing Greater Manchester's first metro mayor and setting up an office for devolution "could cost £5.4m".
A report produced for the area's 10 borough council leaders estimates the election will cost £4m, with an extra £1.4m on wages, rent, ICT and expenses.
Greater Manchester's new elected mayor will have responsibilities covering the police and fire service, planning, housing and transport.
A council spokesman said the "majority of the costs" are "one-offs".
He said they would come from "existing reserves and additional business rates income".
After the initial set-up, annual costs will be about £2m.
These will include the mayor's salary, which is expected to be more than £100,000, the report says.
Plans for an elected mayor in charge of the region's devolved powers were first announced in 2014.
The mayor will lead Greater Manchester Combined Authority, which represents the region's 10 borough councils.
He or she will chair its meetings and allocate responsibilities to a cabinet comprising the 10 council leaders.
The election will be held on 4 May.
Known candidates to date (in alphabetical order)
Sean Anstee - Conservative
Jane Brophy - Liberal Democrat
Andy Burnham - Labour
Stephen Morris - English Democrats
Shneur Odze - UKIP
Will Patterson - Green Party
Local authorities included in the mayoral region: Bolton, Bury, Manchester, Oldham, Rochdale, Salford, Stockport, Tameside, Trafford and Wigan