This website might be useful:
http://www.urlaub-anbieter.com/urlaub-gruppenreisen-gruppenurlaub-mecklenburg-vorpommern-ostsee.htm
Received a quote and possible dates from them (will update later, Ros 18/12)
possible dates: 3. - 10.6. and again after the 15.9. for 16.44 per person and night
looks very good, big common-room and kitchen, 4km to the beach
42 beds in 2-4 bed-rooms, ~15 Euro, linen incl.