Use plywood ! Most wooden rudder stocks break because they are made from planks. These planks break along the grain, often helped by the screws. Plywood is made up of layers of cross grain, this prevents breakage. It took me about an hour to make a new stock from mahogany finished plywood, using nothing more then a power jig-saw, a (battery) power drill and hand tools. Sanding and varnishing it is another story though. Luckily I was able to re-use all the metal parts from the old stock.
I would classify it as an easy job that even a first timer should be able to accomplish.