The findings, to be discussed by the cabinet, revealed 17 "interim staff" were being paid more than £500 a day and two cost more than £800.
Opposition Conservatives have criticised the spending as exorbitant.
The Labour-led unitary council said the expertise was needed to oversee a restructuring programme designed to save money in the long-term.
The council said many of the temporary staff were providing short-term expertise on a project which aimed to save £30m by changing the way the council delivered services.
Conservative councillor Ian Bowyer said: "It seems to me at this moment in time Plymouth taxpayers are being asked to take a tremendous leap in the dark in the hope that we get a result at the end of the day.
"It's far from clear what that result might be."
The council said it was recruiting permanent staff for five of the posts.
Plymouth City Council is paying temporary managers a total of more than £10,000 a day, a council report says.