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.
You can get started homebrewing cider or mead for like $50, especially if what you're brewing isn't carbonated so you can just store it in whatever. You can also buy home garage versions of fully automated brewing and canning lines that will run you into the tens of thousands, not accounting for consumables. It escalates fast.