If you know someone who works at a machine shop, see if you can get their old hacksaw blades. (The ones from the big motorized saws.) I have made a couple of knives out of these and (if tempered correctly) they are easily sharpened yet hold a good edge. I have a friend who swears by old automobile leaf springs.
Whatever you make it out of, the most important step is the hardening/ tempering. Don't skimp on this, do it right!