Old, cheap PCs (like a refurbished Optiplex 7040 for example) are quite nice for this. Depending on where you're living you'll usually be able to find one for $200 of eBay, Amazon or any other marketplace.
Regarding the spec, I'd say
8GB is a minimum, and even better if you can go with 16GB (from my own experience DDR3 is still ok)
Intel i5 is absolutely fine, i7 even better
for storage, you'll usually have to get it yourself, since most machines go on sale with cheap 256 GBs. I'd for a good 2To SSD here, to have some piece of mind. It'll usually cost around $200 as well, so you'll end up at around $400 total. If you're really on a budget a 1To SSD will do for now, but I really think the extra 1To is worth the price.
Avoid RasperryPis, they're not suitable for this task in the medium/long run.
Old, cheap PCs (like a refurbished Optiplex 7040 for example) are quite nice for this. Depending on where you're living you'll usually be able to find one for $200 of eBay, Amazon or any other marketplace.
Regarding the spec, I'd say
Avoid RasperryPis, they're not suitable for this task in the medium/long run.
Happy Node Running!