I sold 7,2 Kg of DDR1/2/3 sticks two month ago, for gold recovery. As well as expansion cards, hdd PCBs and a few other things. Got about $600 from this.
ECC unbuffered DIMMs (9 memory chips per side, no reg buffer/controller) is less available, quite widely used on level entry systems and thus costs a lot more even second hand.
DDR3 is not "retro", for chrissakes.
It was 17 years old, or 14 years since wide distribution in the USA.
What counts as "retro" basically comes down to when the person you ask was born.