If you find the excursions are expensive then do your own thing. It's great fun to explore all of these ports but my advice would be to get on the net and look at the tourist sites for each of the ports to get an idea of what you might like to see. You can also steal ideas from the ship's shore excursions and pick out the things that interest you and leave out the dull bits. If you make friends with another couple or so join up and share a taxi or people carrier and either tel the driver what you want to see or let him take you to the best bits he knows but always arrange a price before you set off. Stockholm and Copenhagen are great to wander around and a harbour trip in Copenhagen was excellent and not expensive. Helsinki is a wonderful place to wander particularly around their markets, we even took a circular tram ride there. Tallinn is just the best, walk to the top of the town and look down at the super roofs and facades then go down to the square and sit and people watch with a very tasty pint of beer. and in Oslo try to get to the park with all the magnificent sculptures in and even in the city taste the clear fresh air, it's special. Not sure about Gdansk but I do know that some of the worlds best dentists are Polish. I must emphasise though you will enjoy far more if you do some preparation.