Let KAYAK do the searching
Based on KAYAK hotel searches, the most popular destination is Copenhagen (70% of total searches to Baltic Sea). The next most popular destinations are Stockholm (13%) and Tallinn (11%). Searches for hotels in Saint Petersburg (6%) are also popular.
KAYAK users have found double rooms in Baltic Sea for as cheap as $26 (Stockholm) in the last 3 days. The average price is $394.