Reform councillors want to see new lease before it is agreed - but have dropped their opposition.
Mayor Ros Jones told cabinet members the main area of overspend was adult social care.
Labour's Ros Jones is urging the prime minister to "listen to the people" following the results.
Polling station across Doncaster are open between 07:00 and 22:00 BST.
Some candidates took part in a BBC Radio Sheffield debate ahead of the 1 May ballot.
Crime, skills and road crossings are just some of the issues for voters in the Doncaster elections.
A guide to the role of Doncaster's directly elected-mayor and the forthcoming council elections.
Richie Vallance says he is "deeply sorry" after being convicted of public order offences in 2016.
Elections are taking place in Doncaster for the Mayor, the council and parish and town councils.
