There have been posts about reasonable barbers in Helsinki. Some of the newer ones do not have a clue how to cut hair, but found the following and he was good and reasonably priced:
HairJaff
Yrjönkatu 29 ( top end of forum)
Price: 14e, students 12e
Open: mon- fri: 10-19.30/sat: 10-19/su 12-18