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.

I still ride my mountain bike from 15 years ago. It requires a yearly budget of maybe 100€ for the usual maintenance stuff, like chains and tires.

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.

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.

Skyrim/Fallout modding. I have never bought a mod, only gotten them from the nexus or made my own.

Wait... those exist?

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.

Mechanical keyboards... You can guess...