Proxmox

The cheapest i5 or i7 with 16GB of DDR3 and an whatever SSD (bcs 50~100 monies for best components of the era, they can idle ok-ish, have SATAs, prob even 5.25" bays for them nice rubber 3.5" HDD adapters since it's provable that you plan to have the PC in/close to your living space).

However have in mind that you very probably have to buy at least one peace of nice storage, such as at least one or two enterprise HDDs (I would say one & plan on getting up a second PC eventually for full redundancy/copy & skip local/raid redundancies).
So that's 100~500 monies maybe, but this already depends on your intended use (or just play with desktop HDDs for a while but they don't last, also smol).

And you might wan't to buy an efficient & nicely built gold PSU (I have mostly used the better Seasonics, but a list like this can help you get you started). Desktops don't usually have PSU for 24/7, might not be safe, and use a lot of power (especially when idling they can have horrible efficiency & affect your electricity consumption).
So another 100 monies but you could get a used one too.

PC is the way to go imho, for a small amount of concurrent uses they are way faster than serves for the same price (you don't need extra throughoutputs, PCIe lanes, or closed sauce megacorp server tools), are very loud, and consume a lot of power (especially old ones don't even really idle/drop the voltages on CPUs).