I just set up a demo LG display that offers elevation, tilt and rotate. The stand is plastic, feels cheap, and is terribly inaccurate as far as level and 90 degree stops are concerned (actually there are no stops), and the display can be rotated about 93 degrees in one direction, and back the other way 94 degrees. Getting it just level is difficult. The lift is on a vertical slider that holds the display in place, but it feels like it's running on old bearings. It sits on a round base about 12" in diameter and rotation is smooth-ish,
So, how much is a good monitor stand worth?
I'll leave that up to the individual who is buying one.
But!
High-quality, precision machined aluminum is not cheap, and neither are high-quality counter balances. Since Apple is shooting for the upper end of this market, it is no surprise that they are using a significantly higher quality stand than can be had from the normal players. That said, let's figure in Apple standard margins, which are roughly 38%. That means the cost to build one of these things is probably in the neighborhood of $600!
Apple makes more on accessories, so I'll be generous and drop that to $500. Keep in mind that this number represents the cost of manufacturing, and does not include R&D, administration, marketing, etc. I would guess that the entire cost is closer to $700, so Apple is making $300 or so on each stand they sell.
There is also a secondary cost to such things: Most people are likely mounting the XDR display on pre-existing VESA arms/mounts and are not buying the stand from Apple. That means that quantities of scale do not exist such that the things can get much cheaper.
To answer your question, the stand costs a lot because it does.
Same with the Mac Pro. Apple won't be selling many of those things, so the costs cannot be brought down through economies of scale. Ferrari doesn't sell many Ferrari's, and Lamborghini doesn't sell many Lamborghini's. They're expensive
because they're limited production. And because people are willing to pay more for limited high-performance things that are similar to commodity things, but with
mostly higher performance characteristics in very
specific usage scenarios.
Also, the biggest complainers are looking for the xMac, which—as was pointed out—is simply not going to materialize. It is no longer worth the argument—or complaint—about such things. It doesn't exist because Apple cannot find a
profitable reason to build it. The Mac Pro is expensive because Apple is a
for-profit company.