(This is a girly post)
Oh yes, there are plenty of beauty salons in Helsinki. I can't personally ever afford to visit them, but many of my friends have got their nails done in especially Kallio, which is as well the place to go for getting nails done. There are many, many nail stores in Kallio, almost next to each other. Prices are around 40-60€ and these stores are owned especially by Thai girls, who are also very gifted in this work. Again, I don't have personal experiences, but I've seen my friends nails and adored them.
Most of the shops are along Hämeentie, between Hakaniemi and Sörnäinen. If you walk along that, you'll see many nail shops, especially closer to Sörnäinen. Then there are few in Porthanin katu.
Again, because I'm focused in urban travelers, I don't even want to mention those 7356749653987€ places (but if you have a black amex, go to upstairs of Stockmann or to Punavuori).