Oh, you guys took the bait.
Key prices were always the same, or at least quite stable (let's say 1.8-2$, idk, i've nerver bought any), excluding temporary changes (like Steam Summer Sale drop).
Keys are fine, but the price of refined has dropped rapidly. One ref was worth ~0.60$ some time ago, now it's price is ~0.35$, so you need more metal to be able to buy a key. Let's call that a metal inflation. Metal devaluation is much slower at the moment and may stop due to anti-idling update.
http://backpack.tf/stats/5002/6/0
People using unusual prices on that website like it's the bible
If they're using - for example - 4 months old crappack.tf prices, it's their own fault.
(Sorry for my English, but it's 4:30 AM here)
EDIT: And yes, I know that a good percentage of backpack.tf users are just butthurt kids. However, all the complains about "raising" key prices are simply annoying.