This is an important point. I have a pal with an aging 5k imac that he wishes he could use only as a monitor with a new mac mini.

It seems display tech in imac is severely discounted in order to sell the whole thing. And it does seem to break the pricing if you don't see them as different products offering value for different configurations.

Bringing back target mode, or allowing the iMac to act as an external monitor would greatly increase the value of that product.

I can't explain how this pricing makes sense exactly, except that I can only assume Apple will want or need to price this stuff high to help differentiate the build quality in comparison to the collaboration on LG's ultrafine.