Elisa (39% market share): unlimited 1 Mbps data for 9.90 euro a month (29.90 euro a month for 150 Mbps).
Telia (31% market share): unlimited 0.256 Mbps data for 7.90 euro a month (29.90 euro a month for 150 Mbps).
DNA (29% market share): unlimited 1 Mbps data for 12.90 euro a month (29.90 euro a month for 150 Mbps).
Moi (part of DNA these days, don't know if it's counted in their 29% or not): unlimited 100 Mbps for 18 euro a month (23 euro a month for 300 Mbps).
I think Moi might be the only operator that actually sells fixed data plans (6 euro a month for 4 GB at 100 Mbps). Everyone else just sells unlimited plans at varying levels of speed with the entry-level plans basically handicapped to basically email syncing only.
Also, apparently the average monthly data usage for a mobile plan in Finland is 34.3 GB (https://blog.telegeography.com/finns-lead-the-way-in-mobile-...). Probably not going to be hitting that at 0.256 Mbps.