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The terrorist attack on holidaymakers on the beach at Port El Kantaoui is expected to cost Tunisia at least a quarter of its annual earnings from tourism.
The government estimate came as the death toll was confirmed at 38, with 30 of the victims thought to be British tourists.
Tourism to the country generated about £1.1 billion in revenues last year, accounting for 15% of GDP. It was the second biggest source of hard currency, the Times reported.
Almost 425,000 British holidaymakers travelled to Tunisia last year.
But leading tour operators are switching programmes to other destinations this summer.
Tunisian authorities stepped up security and arrested several people on suspicion of helping gunman Seifeddine Rezgui, who had links to jihadist group Islamic State.
The Foreign and Commonwealth Office maintained its warning that further terrorist attacks are likely, including in tourist resorts, and urged travellers to be vigilant.