An instrument - you can actually get perfectly reasonable starter version of most instruments for around that price point if you shop around, which will work fine when it comes to gigging too. Guitars, Basses, Midi Keyboards - you might have to shop around, but it is possible to get within the price limit.

I've been learning bass for the last month and a bit, and it has made a big difference to how I feel about myself and my confidence that I can pick up an entirely new skill from scratch, and that I can make music.

With things like LMMS and Hydrogen available, and lots of royalty-free free sample packs available, it is entirely possible to write and perform music on the cheap.

And if you're still not convinced? The tech industry seems to want us to be 'rockstar' developers, devops, admins, growth hackers, etc... so why not literally become one too? ;)