Skip Switzerland and add more Italy to lower your costs.
Go on wikipedia for Tallinn, Riga and Berlin airports (Berlin still has 2) and see where all the low-costs fly to/from. Berlin <>Riga has Ryanair flights which are always dirt-cheap. Traveling between the baltic countries is easy/comfortable by bus (cheaper if you buy in advance, but still cheap if you buy on the day) with the likes of lux express and ecolines.
Finland to Tallinn is an easy ferry ride. Ryanair has a base in Bergamo, not too far from Milano, so see where they fly to from there (again wikipedia is your friend).