My two are:
Making sourdough. I personally always heard like this weird almost mysticism around making it. But I bought a $7 starter from a bakery store, and using just stuff in my kitchen and cheap bread flour I’ve been eating fresh sourdough every day and been super happy with it. Some loafs aren’t super consistent because I don’t have like temperature controlled box or anything. But they’ve all been tasty.
Drawing. I’m by no means an artist, but I always felt like people who were good at drawing were like on a different level. But I buckled down and every day for a month I tried drawing my favorite anime character following an online guide. So just 30 minutes every day. The first one was so bad I almost gave up, but I was in love with the last one and made me realize that like… yeah it really is just practice. Years and years of it to be good at drawing things consistently, quickly, and a variety of things. But I had fun and got something I enjoyed much faster than I expected. So if you want to learn to draw, I would recommend just trying to draw something you really like following a guide and just try it once a day until you are happy with the result.
All you have to do is avoid paying New-In-Box GW prices, and avoid/minimize GW paints and the cost of the hobby drops through the floor.
Tons of skirmish games in all settings are around, many of them with free rules. Battletech is cheap because it basically needs skirmish game amounts of minis. Even playing 40k is cheap(er) embracing third party and scratchbuilding.