ddr4 regged is actually cheaper than plain old ddr4 sometimes. Check the servethehome.com forums and ebayAnd DDR4 is fuckin' expensive. I've got a T5610 workstation from the scrap bin at work that I managed to get working, except now IT wants the RAM back.
And as a bonus, it only takes DDR4 registered ECC.
I don't even use the computer, as I do 99% of my stuff on my laptop, so I don't even want to spend the money.