If you want to make a nice looking wooden one... here is how I made mine... Get some oak, pine and cedar slats from Lowes or Home Depot and alternate them like so...
Then make a jig to get the curve you want. You can use your old broken rudder to trace out the curve on a pice of plywood. Make a jig by screwing some blocks along the curve. Titebond III or Gorilla glue the slats, clamp and let dry. Note the plastic sheeting... You don't want to glue your new rudder to the floor.
Put the tiller in a vice and shape it with a sander or grinder... then smooth with sand paper
Stain varnish and let dry
Now you have a new salty looking rudder... any length you want and as curvy or straight as you want.