>Is there still a whacking great price premium between ECC and non-ECC memory for desktop, but not server, motherboards?

Yes for both.

Price: On pcpartpicker a stick of 16GB DDR4-3200 memory without ECC costs $28.99[2], but the ECC version costs $52.99[1]. Even factoring in that ECC ram comes with an extra chip, it's still 62% more.

Performance: using the same links above, we see that ECC ram tops out at 3200 MT/s, whereas for non-ECC you can get 4000+ MT/s. The brand selection is also better, which is critical if you want to get high performance memory chips like samsung b-die or micron E die.

[1] https://pcpartpicker.com/products/memory/#b=ddr4&E=1&sort=pr...

[2] https://pcpartpicker.com/products/memory/#b=ddr4&E=0&sort=pr...