Yeah I hear you with people wanting pricey sums for withered tech. I have been watching ebay for a few months now trying to grab up a decent server at a decent price but its been sort of a waste of time trying to find a good Xeon CPU server. I thought I found a good deal the one day but when I checked into what generation the Xeon CPU and chipset was it was sadly a Pentium D era Xeon.
A few years ago I saw a neat hack to get a socket 771 to work in a socket 775 with a pad/pin reroute strip in which the Xeon CPU itself without the Server box was cheap, but when I looked into doing this I saw mixed results with some people saying that their BIOS supported it and others with troubles. More info here on that trick/mod:
https://www.delidded.com/lga-771-to-775-adapter/Years ago I would just find a server class motherboard with two Pentium II or Pentium III's and run that. But ever since the server class processors being a different socket than standard computers you don't find dual socket boards anymore that can run desktop class processors with teamed processing power. Seems like ever since the Pentium 4 era Intel and AMD ran off with server class processors specific for server class main boards.
The HP Server I have I haven't powered it lately because its performance to power consumption ratio is weak. When I first got it for free I thought I could replace the dual dual-core Opteron 2216 2.4Ghz with the better Quadcore Opteron 2384 2.7Ghz which also has more cache. This way the server would have 8-cores and around the same power consumption as the original server with far better processing power. Sadly when checking into the motherboard of the server it didn't support this upgrade and only a faster clock dual-core was supported which wasn't worth the upgrade. It came with dual FX4600 NVidia video cards too, but those are good for CAD but not for gaming or crunching for BOINC etc. I removed those cards and put in a Geforce 9800 GT to drop its power consumption but its still too old for what I do.
Friend of mine told me that the single CPU Xeons are pretty decent and they are for power consumption to processing power ratio and have been keeping my eye out for something that isn't too old and isn't too pricey. Been thinking a few times that maybe I could just get the main board with CPUs and install that into a modified tower to accept it but then you have power supply connections to main board that are non standard ( not ATX etc ) so its best to just get a complete server intended for the case that it was built for.
The other thing with buying used is that the shipping fees are up there since servers are generally heavy and bulky so $50 to $70 or more for shipping then the heavy prices that they are asking for decommissioned servers. I feel I am probably going to end up buying a new server "with free shipping" but I need to be at the right place at the right time -or- maybe be lucky to get a better server for free that will take dual quadcores.
