You’re right. It is an extra $100-$150 for implementing mini-LED and extra $100-$150 for a 120hz display. Apple can drop the price to the original $999 or $1299 if it does not include both features that are available on mobile device for years.
$1299 or so is where I think the current display should land at the very most.
Mini LED 4K 32" monitors with 500+ zones and 120+Hz are available this year for well below $2000.
I would have expected Apple to match that in a 5K 27" design with the extra design / webcam / audio pizzaz at $2500 at the most.