Keyboards are generally known about, but the ergo part of it is a rabbit hole within the rabbit hole. Some people literally design, 3D print, wire up, solder and program one-off keyboards because they don't like the ones made by other people.

Maybe not as expensive as the others, but crochet/knitting/sewing all start off fairly cheap, and then the next thing you know you're offering to service old men behind a Joann's fabric because you need this particular fabric and you need an entire bolt of it, and it's the one fabric in the entire fucking store that isn't on their amazing buy one get 73 free sale for the week.

3D printing! You can start out cheap but you can get STUPID expensive, and it’s the biggest most meandering rabbit hole I know of

Gymnastics. The skill part is obvious but monetarily its more than i expected. I thought it would be like going to a regular gym but its usually much more expensive to use the gyms and thats if you can find a time slot where adult males can train.

Magic: the gathering.

There's several different styles of play known as "formats".

The Cheapest being "Standard". Which is the latest 3-5 sets released. The deck of 75 card deck can cost upwards of £500.

Then the most popular format, modern, which is the last 20ish years of release. The average deck there can be upwards of £1,500.

Then there's legacy and vintage where decks are in the high 4 figures and some even in the 5 figures.

I am still amazed about how much money you can spend on making coffee at home. 300€ for a manual grinder - "that's the cheao chinese stuff" wtf

I feel like games workshop table top games(e.g. Warhammer 40k) would fit in to this description if an individual had never heard of table top wargaming, or their reputation.

They're made of plastic? It can't cost that much right!?!?

but the rules, they can't be too complicated? It's just game !?!?

Rock climbing. To start out you basically just need $150 worth of shoes and some $5 chalk. Trad climbing or big wall climbing can be 5 figures and a dozen years worth of experience. And the skill ceiling is probably obvious, but it's become an Olympic sport for a reason.

Warhammer 40k

I don't think the average Joe would know how expensive Warhammer 40k or model trains are.

Warhammer 40k. I heard about the game years ago and thought it sounded pretty cool. Didn't realize that unlike D&D, it's not something generally played without minis. And it's a massive war game. So you need a lot of minis. And it's a massive war game. So you need to know how to strategize or you're gonna suck. High cost and high skill.

I just read the lore instead. 🤷🏻‍♂️

Probably more well known but with the whole 'live edge' fad from a couple years ago now, some people don't realize you can spend upwards of 20-30k on a single piece of some types of raw lumber.

Model trains. Sure, you can have a lot of fun with a 100 dollar toy train, but those brass engines are very shiny and very expensive.

Skydiver here.

It's not just money, it's not just skill that makes you a successful jumper.

It's a certain type of attitude and the ability to think when you've aimed yourself at a planet. Not everyone can do it. To be blunt, there is a large part of the population that shouldn't do it, because they have terrible decision making ability.

As far as money, I went through the student program in the mid 90's and it cost me about $1200, if I recall correctly. My first rig, used, was $4000. My second rig, new, was just over $8000. I have 4500 jumps most of which I paid ~ $20 each for. I don't want to do that math.

I'll do the reverse - I think most people would expect homebrewing beer to be quite hard to get started with, but for $50 you can get everything you need to start making a really quite good beer, and save money at the same time (homebrewed beer is usually much cheaper than store bought)

If you want to get started search for "brew in a bag" and buy a kit beer mix. You'll need a handful of equipment like a brew bag and fermenter, but that stuff is really cheap.

Then you can indeed go down a massive rabbit hole of refinements, but it just amazed me that the first beer you make will already be a good one.

Sim racing. An entry level wheel cost 100, an okay one 300 and the most expensive I've seen is 100,000

https://www.f1authentics.com/products/red-bull-simulator-championship-edition

Maybe it is well known, but home brewing. You start out with a couple of buckets and a stockpot, next thing you know you're spec-ing out a 10hL brewery with your mates. There is always "just one more" thing that you need to buy to make the perfect beer.

Playing music has basically no skill ceiling.

Amateur astronomy, especially astrophotography. Sure, budget setups can be had but nothing beats your own permanent observatory.

Coffee, particularly espresso.

I feel like a lot of people might think miniature building/painting could be easy - or at least quick.

It isn't.

Racing drones.

It turns out when you crash your $500 drone into a brick wall at 50mph, shit breaks and you get to spend more money if you want to fly it into another wall

Model railroads.

They fit both the signifigant monetary input and high skill criteria at the top end of the hobby.

Welding.

Hobby CNC

You can get a little table top router and some simple software for a couple hundred bucks. You can go deep into it. Building a custom machine, writing your own post processor, dialing in you CNC to insane levels of accuracy and precision, adding a 4th axis, engineering parts and projects, it goes on. It basically combines robotics, design engineering, and manufacturing engineering all in one hobby.

Mechanical watches. Most people don’t understand just how expensive they can get, outside of the ones with diamonds all over them, nor why they’re so expensive. Most people also don’t understand how expensive it is to be allowed to buy certain models, depending on the model and the dealer you’re buying from. Also, watch repairs and regular servicing of mechanical watches is something most people don’t consider, and the price of tools if you want to do it yourself can be very expensive and require a lot of skill.

Hifi Audio (headphones in my case) very easy to spend thousands on gear, upgrades, the latest processor or driver technology.

aggressive style roller blades
high skill AND price barriers 💀

Improv theater. Most theaters, even in smaller areas, require 3 or 4 classes before you can audition for a team. The classes usually run around $200-$300 a pop. Once you're on a team, you're required to pay for a coach and sometimes a practice venue. Smaller markets are easier to get onto a team than bigger markets, but there's generally a lower ceiling. Those that are really serious usually move to New York, Chicago, or LA for a chance to do it professionally, which very few people get to do.

Apparently fur-suits are ~$15,000. You could buy a car for that and still have enough money left over to drive for a year.