You can have the complete surface of the bath tub done over again. There are even people who will recolor the new surface. Get ahold of a local plumbing supplier and ask them who they use to make the repairs on their newly installed fiberglass tub and shower units that have been damaged under construction. The technician will come out and give you a quote on what it will take. Its typically about the cost of a new unit, but you will not have all the other associated costs for demolition, reinstallation, and plumbing.