Paper costs, production costs, etc. have all been going up at a rapid rate over the past few years.
I was having a conversation with my younger brother the other day about the price of his college text books. I understand what a ridiculous scam the college book market is to begin with, but he just shelled out 130 bucks for a statistics book last week. That's pretty crazy to me.
Anyways, as I'm sure you can all imagine we sell a lot of books at Battleground. I can say for sure that MSRP on books have been going up steadily over the past several years. Other companies increase prices on their core rule books a couple times a year. Sadly, GW increasing Codex prices does not come as a surprise.