I have booked a 1-2 person cabin on the TT-Line ferry from Rostock to Trelleborg and back. If somebody wants to use the second bed that would cost 42.50 € for one direction. The tickets for a one-way ferry passage are 24€ or 12€ for students plus 3€ eco-extra-fee. Car fees can be found here: https://www.ttline.com/en/passengers/
Rostock-Trelleborg: Tom Sawyer
Sat, 25.07.15, 23:00 - Sun, 26.07.15, 6:00
Trelleborg-Rostock: Huckleberry Finn
Sat, 01.08.15, 23:00 - Sun, 02.08.15, 6:00
In case somebody is interested, I would also like share information regarding the train connections towards Stockholm.