Bought a mid 2010 iMac at goodwill for 15$. It works technically.... : r/mac
Upgrade iMac Intel Core i3 CPU to Core i7 - iFixit Repair Guide
Apple iMac 2010 review: Apple iMac 2010 - CNET
What Does It Take To Upgrade a 2012 iMac 21.5"?
CPU Fan for iMac 21.5" A1311 (Late 2009-Late 2011)
iMac 2009 to 2011 (A1311/A1312) Upgrade Guide – MacintoshMen
CPU upgrade for iMac 21,5" Mid 2010 | MacRumors Forums
Original Tested A1311 Motherboard 820-2784-a 631-1335 661-5538 661-5534 For Imac 21.5'' Logic Board Mid 2010 Year - Laptop Lcd Screen - AliExpress
Amazon.com: Timetec 16GB KIT(2x8GB) Compatible for Apple DDR3 1333MHz PC3-10600 CL9 for Mac Book Pro (Early/Late 2011 13/15/17 inch), iMac(Mid 2010, Mid/Late 2011 21.5/27 inch), Mac Mini(Mid 2011) MAC RAM Upgrade :
Apple iMac 21.5" A1311 Logic Board 820-2784-A W/ CPU i3 3.06Ghz 2010 Free ship | eBay