Executive ministers have clashed over the cost of Stormont's botched renewable heating scheme, with a £110m gap between DUP and Sinn Fein estimates.
It came after Finance Minister Mairtin O Muilleoir claimed that while the outlay this year would be £20m, over 20 years it could come to £600m.
But DUP Economy Minister Simon Hamilton's department put the "maximum burden" of the Renewable Heating Incentive (RHI) on the public purse at around £490m.
Mr O Muilleoir also said he had asked Mr Hamilton's department for relevant documents in July and then again in October, but had only received the papers a week ago.
A statement from Mr Hamilton's department said it had been developing proposals for changes to RHI that "if accepted could lead to a significant reduction in future costs to the Executive".
"Based on a forecast 3% Barnett share of the allocation for the GB scheme, the projected available budget is £660m," the statement added.
"Based on those figures, the maximum burden on the budget would be £490m."
Mr O Muilleoir said the initial £30m that has to be found for the first year of payments could lead to a loss of around £600m over 20 years.
"We know there are people that are scamming this heating incentive," he added.
"I don't want to reward those that have been gaming the system - I want to go after them."
He also warned Mr Hamilton: "If I'm presented with a solution that will save half the money, I will send it back."