Dropped by the hardware store today, and realized that things cost lots and lots of money. like...15 dollars for the angle iron I would need to make the grappling hook, and nothing made of spring steel for the crossbow prods. the new plan is to drop by an auto parts yard and pick up a set of parabolic leaf springs off of a car. the longest spring is perfect for a crossbow, and a shorter one can be used for the grappling hook, with no risk of it bending under my weight. I'll probably try to make knives out of the shortest ones.
For now I've got another tetanus inducing piece of metal I can use to test crossbow design.