Tell him you want a second opinion on that estimate and you'll get it for him..If you just tapped him a 5mph it should just be paint scratch no bumper damage/rips anything. You should have gotten a police report so that you would have evidence that there was prior damage, because all you have is your word against his or a number from any witnesses other than you or him. Any professional body guy can tell if damage was done recently or if any other mods were done before. If it's true about what your saying (5mph thing) it shouldn't be more than $400 in damage. He's trying to get you replace the whole bumper and paint...