Self hosted budget management app is like more advanced user stuff rather than the normal users would do. So hosting that kind of things might sound very weird to you, I get that.
But it is more like a tendency. Most users start their homelab with very basic services like storage management, video streaming, photos, or note taking. There is a huge steep learning curve to run all of them safely and robustly, but once you get over it and there is a wide and very flat area you literally can do anything whatever you want.
Budge management app is like that thing. Many of us wouldn't start hosting budge management app, but we will get there eventually. Because we can.
If you design an application, choosing database would be a big deal, but since you are the user, you can choose whatever you want. My go to is postgre though.