Here are some pics of how I made a rudder out of nothing but brass. It's not the lightest rudder but will get another boat in the water if your on a budget. It is really strong! This one will be going on my wild thing .15 ...when I get it built a little later.
All you need is a small peice of sheet brass and 2 sizes of tubing. I used 1/16th for the rudder blade and swivel mount. 2 sizes of tubing...1 fits inside the other. Can't remember what size these are. Plumbing solder, flux, and a propane torch.

...more pics.

Boy, that takes me back. I used to make my own struts and rudders using the same method but used steel for the blade instead of brass. The only difference is, I found that splitting the rudder post weakened it so it failed easily if it hit something. I changed to slotting the rudder blade and low temp brazing the post into the slot in the blade. Nothing fancy and they work fine.