The repair bill to stabilise cliffs where more than 6,000 tonnes of rock have fallen has leapt to £700,000.
It is likely to be September before the popular Undercliff Walk in Brighton is finally reopened following the latest falls.
Brighton and Hove City Council believes it will have to spend the money to stop more rock falling on to the walkway at Black Rock.
It is £200,000 more than estimates made before the last big fall two weeks ago, when 2,000 tonnes fell on to the walkway and closed the neighbouring Asda store at Brighton Marina.
Among work being considered is an avalanche fence at the base of the cliff, bolting the bottom section and grading back the whole cliff face.
The cliffs are protected because of their geology and rare wild flowers and any work will have to be approved by the conservation watchdog English Nature.
A council spokeswoman said: "Our plans have gone in to English Nature. We expect a speedy response from them, although they have 28 days in which to reply.
"Then it should take us four months to carry out the work to make it safe."
Heavy rain has been blamed for the falls.
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