The cost of closing the troubled East Brighton College Of Media Arts will be more than £4 million.
The secondary school, known as Comart, is likely to shut at the end of August next year.
Falling pupil numbers, high truancy rates and a history of academic failure at the school in Wilson Avenue have made the closure almost inevitable.
But Comart is part of a private finance initiative involving other schools in Brighton.
Chief finance officer Chris Taylor is advising Brighton and Hove city councillors that the cost of removing Comart from the project would be £4.4 million.
The council has had informal talks with Jarvis, the company involved with the private finance initiative.
Costs involve repaying debt, scaling down a management contract and legal and financial fees.
There would be money for the council to pay towards pupils' transport costs if they move to other schools.
The nearest is more than three miles away.
There could also be considerable redundancy costs if some staff fail to find other jobs.
The cost to the council in the next financial year would be £208,000.
This would rise to £489,000 the following year and slowly decline after that.
Paying the debt and other charges would be partly offset by reduced costs for the school.
Mr Taylor said the council could gain income from selling the site which would improve finances.
If it was left vacant there would be security costs.
The £4.4 million figure is lower than previous estimates suggested by some councillors of up to £17 million.
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