It may cost 5.9 billion yen to salvage the suspected North Korean spy ship that sank in the East China Sea in December, sources in the Japan Coast Guard said Thursday.

The estimate includes constructing a special barge to tow the ship and costs that could be incurred if lifting the vessel is delayed by bad weather.

"The cost is equivalent to building a 1,000-ton patrol ship and is by no means cheap," a senior coast guard official said.