Replacement clasps for a mid-size Seamaster 300?

Having a watchmaker or jeweler re-brush the clasp will be a lot cheaper than buying a new one. My wife wanted the bracelet on her Cartier tank restored (polishing and brushing) because it was scratched to heck. It was only $120 and came back looking like new.

As other have said, you can do this yourself, but go slow. It will take some time to do it by hand. Don't get in a hurry and use a Dremel with a polishing or brushing attachment or you will very likely regret it.