Each train, time and date has its own pricing - the earlier the cheaper.
Can't really say that there's a maximum price, but as an example (economy class), booking for tomorrow Helsinki-Tampere, it varies between 16.90 for the local trains (this price is fixed, but a 2h19 journey time on an Sm4 unit). The Intercity prices vary between 21 and 34 eur depending on time, eg: 16h000 departure from Helsinki is 33.90, while the 16h27 is 27.90 and 17h00 23.90. THere are some journey time diffferences, 1h39 to 1h54.
If I try booking for 1st of August, then the Intercity prices are as low as 6.90 with the most expensive at 21.90 - most are around 11-13 eur. Interestingly the local trains are still 16.90 due to their fixed price.
So, the same day fares are the highest you can say.
Oletko suomalainen? Sinun "nimi" on suomeksi...