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You can always check the Kampuferry website for their fares and information.
Keep in mind the port facility charge and fuel surcharge, which are settled only in cash and collected directly at the counter of the company at the time of check-in, both in the Shimonoseki port and Busan port.
On that website you can also read about the Passenger Tax for Promotion of International Tourism. It's 1000 yen, cash only.
Collection Passengers over 2 years old departing from Shimonoseki
Location Check-in counter on the 2nd floor of Shimonoseki International Terminal
Amount 1,000 yen (cash only)
Start date of collection : January 7, 2019 Customers departing from Shimonoseki