I haven't checked, but I'll have a look next time I play.
Edit* I played the DH today for about 2 hours, as well as browsed many websites forums etc. I have downloaded 85mb and uploaded 24.54mb in that entire time (including web browsing). I'll do a more accurate measurement soon without the web browsing
That works out to ~2.8 KBps (or is it Kbps? I don't know what the megab's we're in your post). Either way, not a lot of bandwidth required. Downloaded is probably going to be a lot harder to calculate with the web browsing
I'm sure 1 hour game traffic is going to be way less than 1 hour of normal web browsing, game usually move just a couple of KB/s up and down as far as i know, at least with left 4 dead it goes around those numbers if i recall correctly.
Back when I was close to my download limit and had to take note of daily usages, I found myself just doing nothing online but playing SC2 and I was blown away with how little it downloaded. It was about 20-40 megs per day. That included browsing on this site too while I was waiting for coop to pop. I played for about 4-6 hours or so each day, over those days.