The reason they want that much is most likely because they are going to not only change the battery, but to a pressure test to make sure that there are no leaks. When you buy a good quality watch from either a jeweler or a watch specialist, they will tell you that anyone can change the battery but if you want the watch to last after diving with it they will tell you to do a pressure test. I have family in the jewelry business and they are also dealers for Rolex and other fine watches. I have had to find this out the hard way with a watch that luckily wasn't a Rolex, but was damn expensive.