I started out using Obsidian just for university related stuff but found it incredibly useful, so I ended up purchasing the license myself. While I'm not a big fan of subscription software, 50$/year is extremely reasonable, especially considering that your data isn't trapped in someone's cloud.
Just a side observation: Many people on HN do make money building software, yet so many users seem completely unwilling to pay for software. In some regards I do understand that, there are quite a lot of "bad companies" out there that you just can't avoid in many circumstances, but as far as I'm concerned, Obsidian seems like the good guy (for now at least).
Paragraph 1 in the EULA - https://obsidian.md/eula - say "You need to pay for Obsidian if and only if you use it to contribute, directly or indirectly, to revenue-generating, work-related activities in a company that has two or more people"