Did you tell him the bumper was made up of sections, and you only wanted to repair the damaged section? If they only saw the picture of the bumper on the car, and you didn't point out that the bumper blade is about 36"' long, that would have caused them to over estimate the repair and replating. I know that the last time that I had the 3 piece bumper for my 1962 Chevrolet done, repair and plating for that bumper end was $300, and it is about 33" wide. Measure the blade itself, and give them that information and ask them it that will effect the price that you were given. I have always found that they were very competitive. Possibly Dan can take a picture of a blade so they can actually see the individual part, or you could use the picture of the bumper parts lying on the floor that he provided you.
Paul