Welding. I used to give my iron things which needed some welding to my best friend until he has moved. Then he told me that it is not that complicated, especially because I have already had some experience with a corner grinder (the cheapest and easiest way to cut some metals, but safe and precise cutting requires some skills). So, the cost of MMA machine plus several kg of welding sticks is 150$ and after few weeks of practice every day after work I have became able to do some basic stuff from first try. I have never had an instructor who has been watching me while welding and showing me some do and donts. But when I had some obstructions, I could phone to the friend and ask him some questions, like where to get some metals and how much amperes to set. I do not thing it is just from word-of-mouth because it required me to do a lot of practice but you do not need any welding courses if all you want is to construct some shelves and repair some easy things.

Since I'm not in an office, most of the people I actually talk to are friends and family, and that stuff tends to be private, or hyper-local, new places to get food, etc.

I'm afraid with all the lockdowns, most people will have similar answers.