if you want a really cheap knife that is decent quality, you can get a rapala bait knife for about $5 US at the local sporting goods or fishing store. mine has a serrated back for scaling, and it is good for cutting notches into sticks and things. i picked one up near the end of summer, and have since turned the blade into a flatgrind profile from the shallow hollow grind. i also wrapped the bright white handle (good for woods finding) with some black electric tape. i have also considered dipping the handle into some plastic tool handle dip, which would better the grip.
this is a great knife if you want a real beater for messing around with, and it is pretty sturdy for all sorts of stuff.
just shy of 4 inch blade, by the way.
a note: i have no affiliation with this company in any way, i am just impressed with the quality of the knife for the money
otherwise, from what i have read, all of the before suggested are good knives for the money also, if you want better quality than the bait knife.
i know that if you are on the cold steel mailing list, you should have a holiday flyer advertising good sales prices on a few of their knives.