Not sure if you’d call it a hobby or more of a collection but I collect mechanical wrist watches and that can get expensive fast.
I started with a mechanical under $100, with a decent movement and a display back case so I could see the gears and rotor inside, and that could’ve been it. But once you get the bug, you want to get different types of movements, different case sizes, maybe some complications, sooner or later you’re going to start wanting some hand finishing, and then it gets really expensive. I wanna get into mechanical watch repair too but that gets really expensive and takes a lot of skill and time so I’m going to hold off a few years I think. Plus once I go there, there’s no coming back. I’ll be buying broken stuff on eBay constantly and there goes all my paycheques