PSA: the rack at my local Goodwill in Dayton had 3 working Dell OptiPlex towers for $12 each
I grabbed one and it booted straight to BIOS with a 500GB drive and 8GB of RAM already in it. What's the best flip you've ever snagged from a thrift store?
Those OptiPlex towers are solid little machines but the 500GB drive and 8GB of RAM being "already in it" isn't really a freebie, that's just the normal base setup for those things. Dell shipped like a million of them to offices with that exact config, so it's not like someone hooked you up. Still, $12 for a working tower is a steal no matter how you slice it. My best thrift find was a vintage Pioneer receiver for $8 that sells for $150 on eBay all day.