Maybe you have priced it wrong? I just checked Ebay, a 16GB 12800 Registered ECC module goes for 40-50USD ea. That is crazy! Last year they were like 5 USD each.
Except almost nobody buys them, even last years for 10 bucks each. That's almost useless ECC Reg memory for HPE Gen 8 servers and workstations (from before late 2015 / start of 2016 with the introduction of the Gen9 using DDR4).
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.