Aurora periods are generally between sept to early April. But the problem with autumn is that the sky is usually overcast with plenty of rain, so even if there are lights weaving above your head, you most likely won't be able to see them. That said, even if you go in winter, if its cloudy and snows all the time, you won't be able to see it either.
Norway is indeed one of the more expensive Scandinavian countries. But they also have one of the most breathtaking sceneries. How about a cruise along the coast of Norway? I think Hurtiguren (can't remember the spelling) has a couple of interesting cruise itineraries. They are not cheap, but they go for a few days and at least accommodation is accounted for.
Personally I was toying with the idea of this year end flying to Bergen, then take a cruise to Tromso for the northern lights, and then fly to Stockholm, stay there for a few days and take another short cruise or ferry to Helsinki to visit a friend. But at the same time, I was also thinking if I should skip the auroras this time (December is generally not the best time to catch auroras as it snows pretty often, i.e. there are clouds) and spend the Christmas week at my friend's place in Finland, and then another week at London for the new year. Decisions, decisions.
Anyway I'm a little familiar when it comes to Finland, so if TS needs any help regarding Finland, please feel free to ask.
