I’ve always liked this windvane self-steering gear…
Back in the day it worked very well for a lot of cruisers. Sure it can be improved by making t more complicated but for a well balanced boat and a sailor who knows what they’re doing it does the job just fine. Pretty much anything you need to know to build it can be sussed out from the photo and a couple of hours of thought.
While a kiss more complicated there’s a lot to be said for the Moitessier inspired Trismus self-steering vane.
Great if you have a transom hung rudder or adding an auxiliary rudder to the mix. Anyone interested can find some very simple plans that tell you everything you need to know here.
Either vane gear will get you across an ocean and at a DIY cost of a couple of hundred bucks it’s well within even the most frugal budget.