For performance per dollar nothing beats used enterprise gear due to how little you can pick it up for on eBay. Now if you live somewhere where electricity isn’t stupid cheap or you don’t have a good way to mask the sound of a 1000 angry hornets, then enterprise might not be the way to go. Dell SFF PCs can make good servers. You can also go a long ways with just humble raspberry pis, get a whole bunch of them and you can use that to learn K8s too
If you can get a laptop with a few USB ports that can go a long way to helping with storage expansion. Try to avoid USB drives and SD cards, but attaching proper SSDs and HDDs with a USB caddy is a great option. Just don’t accidentally pass the boot drive USB controller to a vm like I did once.