Any of the Hotels near the Airport offer "DayRooms" however they might not be any less expencive than havint ghe room overnight, sometimes these are even more expensive. Check out the following webpages: http://www.bonusinn.fi/ http://www.hotellipilotti.fi/
cumulus.fi/hotellit/airport/fi_FI/airport/ http://www.ramadahelsinkiairport.fi/