i bought a server on ebay a few years ago for plex and game servers after seeing Linus' server videos like the $650 workstation video and every now and again id upgrade the server to the point it can game and still host game servers while ruining 1080p plex streams.
parts list (exc storage)
2x lga1366 xeon e5649 34.95
Intel Server Board S5520HC 49.99
32gb ecc 8x4gb ram 41.99
gtx 1060 6gb 275.00
lsi 9260-8i 57.00
EVGA SuperNOVA 850 G3, 80PG 139.97
In-Win IW-PL052 case 91.92
2x INTEL E97384-002 £45
i put it up against my current build
ryzen 1600x 3.95ghz
16gb g.skill rgb 2400mz
gtx 1070 evga sc
firstly i put it against my pc at stock with cinibench and the server was 12 points behind
then against my oc 1600x
next i used timespy
my gaming pc got 6068 while my server got 4243
in all getting and upgrading a server off ebay i got for £100 to start off with which came with a raid card plus 2 650w redundant psu could be used for a gaming platform on the somewhat cheap ( i got 2 60gb ssds off amazon for about £20 each (raid 1) and 4 500gb hhds (raid 5)) build that can run most games i can throw at it and also run plex and game servers at the same time