ES/QS/OEM are not 'just' second hand :- ) I am not sure we can publicly suggest people to buy them, there is a risk in using them (and I don't mean the legal part...), and they are not identical in many more things than people assume.
Those you mention, I have few of them, most have locked all-core turbo bins and make worse Workstation chips. They are excellent render node value/performance....that's obvious though ;- ) Yup, machine with those goes for around 2300 +/- euros in total (2500 if you want 64gb ram).