Whats a hobby/craft that you wouldn't expect that has an incredibly high ceiling either monetarily or in sheer skill?
For example, I'm sure the average joe doesn't know just how expensive calligraphy pens can be, or how deep the rabbit hole goes on video game speedruns.
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.
From my experience, it's not that much cheaper, especially after considering time cost. One issue with it though is that you get a lot of the same type of beer, which isn't totally bad but also somewhat puts a stopper on trying new beer. It's great if you've got plenty of people to share it with though, but I don't have enough that enjoy beer.