There are all kinds of places to get the vinyl top kits. Since I live within driving distance of The Paddock (no shipping and handling for me) that is where I would get it. If you visit their site, they can get you a free catalog out to you and it has almost everything you would ever need for your classic mustang.
www.paddockparts.com Real nice people too!
The molding seems to be the most expensive part of the vinyl top, $60.