The main advantage of ECC is reliability so buying used RAM doesn't seem like a great option. If you're willing to buy used a good way to get a nice workstation

The main advantage of ECC is reliability so buying used RAM doesn't seem like a great option. If you're willing to buy used a good way to get a nice workstation is to just buy a used workstation machine (e.g., HP Z400/Z600/Z800 line) and just upgrade the storage and GPU. But if you're gaming or trying to upgrade a home server what you want instead is a nice Motherboard/CPU/RAM combination. Right now Ryzen would be a great option for that if there were some good ECC UDIMM options.