Cooking. I have accumulated good cookware through the years and I don't find myself wanting anything new. The only expense at this point is good quality ingredients, but I only eat meat once or twice a week so even that doesn't get expensive.
As a tradeoff, cooking for yourself also saves quite a bit of money compared to eating out. You'll spend more on ingredients but less on staff to prep and clean and serve. And with a enough practice, some of the food you make can be better than what you get in the restaurant. 🤭
Coffee. It CAN get extremely expensive, but importantly the expensive parts can be re-used for decades, and also there's a bit of a bend point in value for the hobby.
Once you get a $150 really good grinder and start grinding whole beans every day, you've gotten 40% better. Then maybe a Chemex or Aeropress for $50 and a weight scale for $20 and you're another 30% better. After that...it's easy to spend $300+ at a time on better equipment or getting into espresso but each thing is like a 5% improvement. You'll notice, but if you don't have much money, it's not really worth it.
And the beans SEEM like they're getting expensive but a bag gets 2 weeks of coffee for me, $20 for really nice beans just isn't that much per cup.
Writing lore is pretty cheap unless you start getting very into fancy notebooks for it.
My, my daughter and a couple friends like writing stories set in fictional works and sharing them.
Honestly other than that...
I put down £50 on a raspberry pi to lean about more about computers when I started a new job.... I'm trying to find a grand to upgrade my 3 pi homelab into something with a few more teeth.
Cross stitching is an extremely inexpensive hobby. You can get started cross stitching for less than $20, if it's a small project. It does require a lot of time as a tradeoff, but can be a very fun way to express your creative side and make cute gifts for friends.
If you have a computer, learning to program is literally free. It'll take time and discipline but I personally enjoy it and the mental challenge it presents.