http://www.bladesandbows.co.uk/armex-tomcat-mk2-80lb-self-cocking-pistol-crossbow-2143-p.asp
I've got one of these, £30 now! That's bang for buck. It can punch a hole in the steel kickplate at the bottom of the doors at work, or put a metal bolt about 2 inches into a tree. If I caught someone in the act of stealing my car I'd have no hesitation in sticking a bolt in one of there limbs. Quick to recock too.