Oddly enough, I just saw a news article about a UK laser defense weapon that can fire a burst of energy at incoming missiles and aircraft. The article doesn't mention the cost of the weapon itself (which, considering development and testing costs, would be substantial) but DOES mention that a 10-second energy burst costs about $13. USA defensive missiles cost a seven-digit number. Laser weapons also have no shell casings, no breach issues, and no ammunition stockpile. The worst that could happen would be that a very large capacitor blows up, but otherwise it is a remarkably safe weapon for bystanders (at least, if they are not in line of fire...)