Lots of different scenarios around here. I know some people that buy them on a head per day basis, anywhere from $0.35 to $0.40 per head per day. We buy ours by the acre anywhere from $15 to $25 per acre depending on quantity and quality of stalks. Obviously sweet corn stalks are better feed than dry corn, but dry corn last longer.
You still need to supplement on them though. We feed hay when the stalks get covered with snow, and use Anipro liquid supplement the whole time.
I would rather graze cornstalks than feed them baled, they sort out the "junk" too much.