They're still incredible money, given their old'n'crusty status.

https://www.ebay.co.uk/sch/Apple-Desktops-All-in-Ones/111418/i.html?Release%2520Year=2013&_sop=12&_dcat=111418&_nkw=mac%20pro&LH_Complete=1&LH_Sold=1&rt=nc&_trksid=p2045573.m1684

Note that the above query is just not for a bunch of chancers asking optimistically high prices - that's actual sold boxes.