A good place to get reasonably priced servers can be 5-6 year old server models from Ebay. The reason for that age specifically is a lot of corporate replacement cycles around servers are typically 5 years. So go look for servers about that old as most company IT departments will strip the servers of drives and send them to recyclers or 3rd party sellers. Right now, you can find a ton of 13th gen Dell servers(T330,T430, R430, R530, R630, R730, R730xd, ect...) for right around $500-600 USD. If you get lucky, you'll have some RAM, if not, low spec DDR4 registered ECC is also cheap for similar reasons as the servers.