Crocheting/knitting is cheap to try out but once you really get into it (and start worrying about yarn quality and so on), the money pit opens. Ask me how I know.

Not no-cost but cooking, gotta feed yourself anyway might as well have fun with it

Drawing, pencil and paper for start and drawing tablets are not that expensive for starter ones and there's free open source drawing software.

D&D costs $90 for the hard cover core book set and $0 for the pirated pdfs.

Biking can have a high upfront cost, but I've been using the same bike for 20 years with tune-ups and replacements running in the low three figures over that time.

I'm a big fan of podcasts, particularly ones that cover old movies. Criterion collection films are everywhere, they're dirt cheap, and they're classics for a reason.

Drawing (we should stop pretending one need expensive material do draw nice things, pencils and erasers are the only requirement, and a good sketch book can be found for less than 15 bucks)

Hiking? I mean, the world is just out there.

Other outside activities that need minimal equipment come to mind. You ever played discgolf? Or went running? Or geocaching?

But yeah, lots of activities aren't expensive. Draw something. Paint something. Sing! Or do some sports! Yoga only requires a mat if you do it naked.

Software development is free if you already have a computer

"needles/yarn after cheap"

That's a lie. My wife is into knitting and crochet, I've seen $300 purchases for yarn only, for just one dress. Not to mention $50-100 needles or swifts or yarn caking tools

Writing (free)

Maybe if you only write in dirt with your finger. Orherwise you need writing implements and something to write on.

Actually free things you can do:

• Walking/running

• Stare

• Singing

• Collecting rocks

• Stare

• Sleeping

IMO piracy and self hosting has great cost benefits.

Sure it costs money to buy a mini computer and a hard drive, but after, you can spend a long time building that library and it won’t cost you a dime.

And the computer and hard drive is more like an asset, you don’t really lose money when you buy it.

And it kind of pays you back, eventually you get a little tired of building your library but then you can use said library and integrate it into your lifestyle while you get a new obsession.

There are plenty of hobbies where you can happily enjoy it and only ever spend little if anything.

On the other hand, I've found it's pretty uncommon to find a hobby where you can't optionally fall down an expensive rabbit-hole of some kind, usually around any kind of equipment or tools you might need as part of some hobby.

Thankfully for most hobbies that kind of thing is not required to enjoy it. You don't need a fancy guitar to enjoy playing; you can read books from the library, you don't need to collect your own; in most big enough cities (in Europe at least) you don't even need to own a bike to go for a cycle (though regularly using bike rental schemes might be a sign to try and get a bike, doesn't need to be fancy)

Entirely seriously, learn how to make a game in Godot.

Its literally completely free, only costs you time, and assumes you have at least some kind of existing computer, doesn't need to be a monster rig.

Alternatively: Find a video game you like.

Make mods for it.

Here's another one that's basically free:

Becoming/Staying fit, gaining strength and agility.

Make 'weights' out of milk jugs with water in them.

Maybe get a resistance band or two, they're not that pricey.

You can absolutely do a ton of stretches, calisthenics, and light to modetate muscle group workouts with basically just random shit lying around a typical home or apartment.

You can find basic guides for these excercises often just freely available from reputable medical organizations.

You can literally just go on a 20 minute walk, 3 times a week, and be in better physical shape than something like half of the US adult population.

Back to computer shit:

Blender is free.

Learn 3D modelling, rigging, UV wrapping, how texturing works, how to make animations, etc.

Same with Krita.

Become artist. Draw stuff good.

You can find probably literally millions of free tutorials for how to do basic and intermediate level concepts.

Whsitling/Singing/Voice Acting.

These are developable skills much more so than they are just... things you either can or cannot do, for some reason.

You can teach yourself how to do these, again to a basic or intermediate level, for pretty much free.

Same thing with at least some kinds of dancing.

If you're feeling more EXTREME: Parkour and/or Urbex.

Lockpicking.

Go find the Lockpicking Lawyer on youtube.

Pretty sure he can recommend you a not too pricey basic starter kit for learning the basics.

... I could go on, but my hands are tired from what I'm going to call 'autism posting', one of my totally free, personal hobbies that I often indulge in.

Ceramics is stupidly cheap to get into. All the tools can be replaced with your hands and a needle, finding workable clay in nature is stupidly easy if you know what to look for and even the garbage clay can be made usable. Most ceramic shops let you rent a shelf on the kiln for like $5. Your first ceramic statue is literally 2 hours of research and $5 away no matter where you are in the world.

music, cooking, public librarying (that's too complicated for one post)

Cooking is basically better than free.

Yes, ingredients and equipment cost money, but the end result averages out to be cheaper than if you didn't know how to cook. And even if you take on more expensive ingredients or tools, you're probably offsetting even more expensive restaurant meals that you would've eaten.

Any art or craft or sport is pretty much free when you weigh up the hours vs the outlay required.

Except skiing and motorsports. That eats money.

Papercraft is pretty cool. If you have some thick card stock paper, a printer, a knife, and some glue, you can find 3D designs online for almost anything. I made an IL2 Sturmovik.