If Arsenal only got 40m for Cesc, I'd be devastated. In my opinion he'll be one of the greatest midfielders in the world over the next 10+ years as his game has nothing to do with speed so you're getting 10 years of world class Cesc, for 4m per year that's daylight robbery. I'd be asking for 60m, see what they're really made of.
I'm pretty sure Arsenal wouldn't put a price tag on a player and then make it public knowledge. I'm fairly confident Cesc will be with us at least 1 more season.