Is the zipper broken on the window itself or on the actual top...or both?
I broke the zipper on my top where the rear window zips into. I called a couple apholstry shops and found one that does work on boats, like daggo said. They said to replace the zipper would be about $150. He also mentioned that the condition of the top would make a difference. If the lip that the zipper is sewn into is old, worn or rotted he would have to reenfoce it so the zipper wouldnt rip out, and naturaly that would cost more.
Just for a heads up on a price range to expect