The budget is way too low imo.
You could repurpose an old workstation, bought dirt cheap on eBay if you are lucky, but even then you’ll have to get yourself an HDD, maybe multiple of them if you want to have data redundancy.
For anything new your best bet is a 2 bay ready made NAS, but you’ll have to invest around 300€ for the cheapest one.
Yeah, for that price you won’t find anything new. For illustration, when I bought a new Athlon 3000G, which was the very lower CPU on their AM4 offering, it was at 55€ without anything else.
Core or Scale ?
With encrypted backups of course.
I never had any problems for almost 10 years outside of a few major outages (that every provider has from time to time).
May be a bad usbc port on one end. My old Nokia 8.1 was known to have a bad usbc connector (mine was impacted), and I ended up switching smarphone because of that. Now I’m waiting for my new phone once again (Fairphone 5), at least this one is easier to repair 😅
Both Anker and Ugreen does good GAN chargers, but Anker is bad at doing good cables (2 of 3 usbc to usbc cable failed during the first year of use). I only had 1 cable from Ugreen, and I don’t use it often, so I can’t tell if they are good yet.
Other than that I don’t have much to say about small electronics, except maybe avoid Asus Laptops. Got 3 of them during my lifetime, all got pretty big problems, ranging from bad screens to dead touchpad and motherboards. They even forgot to connect the internal audio cable during the motherboard replacement, had to sent it back a second time 😅.
Bought 3 laptop from them, all had QA issues. Never again.
My only Asus hardware that works with no issue is my current access point.
Steelseries is a pretty good brand, especially in the premium headset side. Works well on Linux too.
You could run a WebDAV server, like Nextcloud.
On windows it supports thin sync (meaning that it keep a reference to the file instead of the whole file), on Linux not yet, as it is still in alpha (but you can just connect it as a remote disk and be done with it. That’s how I do with mines).
If you don’t want the whole Nextcloud, there are standalone cli WebDAV servers.