Making electronic music. You can get lots of software tools for free, so I started out with those.
Then I realized how many details get lost, depending on what speaker/headphones you use, so bought myself higher quality headphones. As in, quite high-end for normies, but obviously, I'm at the lower end for music production hardware.
Now I'm considering buying a MIDI keyboard, because those software tools don't quite emulate proper piano playing. Although, you could obviously also spend money on getting different software tools. And of course, on a quadrillion plugins for these software tools, to produce different sounds.
I'm just glad that my other hobby is programming, so when my music-self gets excited about an idea, my programming-self will want to solve it.
...and then never finish what music-self wanted, but at least we're distracted from spending money.
If you're wondering, because it doesn't sound like I've actually spent much money yet, yeah, I'm generally quite frugal. I'm mostly just intimidated by all the options to spend money.
But well, my setup is:
Laptop running Linux (that already rules out buying most VST plugins, as those are often Windows-only).
Headphones: Sennheiser HD 560S (←only real money, I've spent so far)
For a DAW, I've been dabbling with LMMS. Felt more approachable to me than Ardour. I also enjoy dicking around with Surge-XT as one quite powerful VST/LV2 plugin.
I'm a traditionally trained musician, so I also enjoy creating electronic music via sheet music. And me being a programmer/weirdo, I like Lilypond for that (basically LaTeX for sheet music), despite it not being built for that...
They're generally said to deliver the sound-quality of medium-grade studio headphones for the price of low-grade ones. But that also means, aside from the sound quality, these are really basic headphones.
You should also mind that they're open-back. So, they have no noise cancelling, neither active nor passive. You have to use these in a silent room.