If you are a tinkerer, one of my favourite things is to find old knives at pawn shops, junk shops or antique shops. Fixed or folding, extra cheap if you cannot open them easily or at all. Typically I can buy these very cheaply, often 2 or more at a time. Within a couple hours of a lite oil soaking and elbow grease, I end up with a very serviceable knife I can add to my collection or even give away to someone who doesn't know they need it yet.