A new hatch for your boat would run about $600.00 Installing Lexan would give you more light and would be great on rainy days to sit in the cabin and watch the rain bounce off it, but it could be a big disadvantage in that you couldn't stand on it if you were raising/lowering your mast, and if the lens doesn't sit low enough on the hatch, it could interfere with the clearance needed to step your mast from aft. I would try to reconstruct it. A couple of good books on that subject are; "Sailboat Hull & Deck Repair" and "This Old Boat" by Don Casey. Your library may have these books. My hatch is cracked where it slides in the groove of the two Teak moldings and I suspect that I'll have to do something to it someday soon. Another option is to bring it to a good fiberglass repair man. Good repairmen are hard to find. The best one in my area is a part owner of a local boatyard in Dighton, Ma. I've seen his work and it's excellent in both the reconstruction and Gel-coat color matching. So you may want to go that route. I've found that fiberglass reconstruction is fairly simple, but Gel-coat matching is almost impossibe without the right equipment and know how. Good luck!