How much would it cost

That would depend on how much you spend on the bumper and where the work gets done. You could buy a new bumper at a dealer, expensive; or look around on ebay, craigslist, or local salvage yards and get a used one cheap. You could do the work yourself for free, or hire a shop to put it on. A body shop would most likely be much cheaper than a dealer for labor, a local shade tree mechanic would be much cheaper than a body shop.