Hi there!
I am not sure what you have written in Finnish as I dont understand everything. Just the basics... But it seems you were crying out for some accomodation in HKI? Well, if you are, there are 3 hostels for grabs.
1) Hostel Mekka (4 bed Private with shared Bathroom) 21.88 a night
2) Hostel Stadion (under the Olympic Stadium) (12 bed male dorm) 16.00 a night
(This is an ok hostel. Some Australian mates stayed here when they were on a Euro tour)
3) Airport Hotel Bonus Inn (can be a touch expensive) 60.00
your best bet is to use the superb websites:
www.hostelworld.com
www.hostels.com
Every Traveller accross the world survives on these and of course, the entrusted data in the "Lonely Planet Guides" and the "Let's Go" Guides.
Good luck... and watch out for the small print of any hostel. If they enforce a harsh "Curfew" then they may close the hostel doors between 2am and 6am or 7am... meaning that your stuck outside till then! :)
Failing all of this... Just go to Hotelli Vantaa where its another Viking Line Boat but on shore. Your bound to hear some suberb band like Popeda ;) and meet a middle aged lady to take home... (aweful place!)
Cheers!