The cost of forging a knife,say from a coil spring or a good file should be dirt cheap.The only thing you would pay for would be the handle material if you dont have any on hand, pin stock,epoxy,and your fuel.The sheath and leather stitching tools or kydex are not bad either.Mostly it comes down to the cost of your labor.Things can get pricey if you move up to making a lot of pattern welded steel.A press or power hammer,the main investment,how good of a belt grinder can you afford ,salt pots high and low temp,ect.,ect.