I've never been to any of these places but they are all cities I'd love to go to I would imagine Krakow would be the cheapest and Stockholm would be by far the most expensive.
Have a good trip wherever you go
Well duh I recommend it as well because it's in my country I've been there and I gotta say that I liked there
I wouldn't go to Stockholm, cold and so damn expensive (my mum's been there and she complained a lot about the high prices)
Berlin, I haven't been there but that's gonna change within the next two weeks I've heard it's a nice city with lots of things to see