Data was released as a response to FOI request. Finland might be the first country where annual subscription fees for all individual publishers and all major research institutions have been made available, spanning the years 2010-2015 (link to the data can be found through the first link and the last link of the following pages).
Release notes: http://openscience.fi/-/transparency-and-openness-to-scienti...
And data: https://avointiede.fi/web/openscience/publisher_costs
For example, publisher Taylor & Francis has costs have increased more than 20% per year in 2014 and 2015.