Wait a second- "the board things on top of the hull..."? You have a GCat 5.0 Mk I with the one-piece hulls and plywood decks? If the fiberglass is in good shape, there is nothing wrong with those hulls. The plywood just bolts into the fiberglass with some bedding compound to seal it up.

Where is the dent in the mast? You can replace the mast with one from a H16 -just swap your base onto the "new" mast. How could it possibly cost you $500 for new standing rigging (including trapeze wires)? If there is a West Marine nearby you can easily swage all your own wires.