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.
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.
Here's one I found in my email: