Before anyone goes "OMG I could use it as a desktop" $75 is close to what you would pay for couple year old ~4 faster laptop with broken screen, sodimm and PCIE SSD slots. Quick ebay check shows things like $90 'Dell XPS12 i7-3537U 8gb 128GB SSD broken screen'
Maybe in the US. In my EU country(Austria) second hand hardware prices are through the roof. There's no way you're getting anything half decent from the last decade for $75. And then there's the cooling and power consumption difference between a 10 year old system and a RPi. It's not even close.
Curious - any thoughts on why?