I built a rudder. Took something like two weekends (first to build, second to fair and paint - something like that).
And, as I was starting without template or instructions (having never built a foil before), one more weekend for design + planning.
I went for rough&ready as far as the materials were concerned, partially because I wasn't sure whether my design would work. It does, so I wish I'd upgraded to a better grade of plywood... other than that, no regrets.
I wrote up the details for the DS quarterly (if you have the old issues, around 2012), but also posted
notes here on the forum.
As I started with a stock rudder, I kept the tiller. It's solid ash, tapering to something like 1"x1" (or just a bit beefier) at the handle part, and something 1"x (1.5" wider than the rudder neck). The end at the neck of the rudder is a fork, with the "tines" about .75" strong. It's held with a single throughbolt, positioned so that the tiller can swing 260 degrees to fold back along the rudder for storage. There's another bolt or rivet right where the fork starts, to prevent the wood from splitting - you could easily make the fork tines from separate pieces, glue them on with epoxy and then bolt them with a pair of through bolts.
The picture of the finished rudder shows the details - the new rudder neck is a tad too wide, so the tiller only swings 250 degrees or so. Not very visible, but a key detail is a little stopper at the front of the rudder neck that prevents the tiller from being pushed down below the horizontal, where it would rub on deck or coaming.

Click to enlarge.
The big bolt for the pivot is a substantial carriage bolt with wing nut - I fitted a nylon bushing in the rudder blade. Thinner/longer carriage bolt with wing nut for the tiller. If you don't have pintles that you can leverage from the old rudder - get a pair with the lower one longer. Makes all the difference
Not very visible in the image - some means to prevent the rudder from jumping out while underway. Some drill through the protruding end of a pintle and fit a cotter pin, I rely on a spring (a blade that is screwed to the rudder and catches the upper gudgeon unless depressed - in the picture, the part is still attached to the old rudder). For belts & suspenders, there's another piece, a small SS angle that sits on the transom where gravity will pull it so that it won't let the upper pintle rise; for removal, it's simply pushed aside and rotates out of the way.
Anyway, the whole project is something you could still get done before the season starts, and the foil shape will be tons better than a stock rudder, and the whole thing lighter (weight at the stern is never a good thing).