What makes a $20,000 cd player cost 20,000?

Pertaining largely to the question of who would buy such a cd player, read "The Millionaire Next Door"; most persons with net worth wealth (not just high income coupled with high expenses and low net worth) would never dream of spending so much on electronics. There are exceptions, but typically the truly wealthy live very conservatively. That would put the majority of our systems, and even many individual components, beyond what they would spend.

In some ways, I'm sure there are audio junkies who can be compared to the person living in an apartment, who has no savings or retirement plan, yet is driving on lease an expensive automobile. The appearance of wealth, without wealth. So, many audiophiles probably have high end systems but are not net worth wealthy. They are the one's more likely to buy the $20,000 player. High income coupled with a high cash burn rate.

I'm sure there is a discernable difference in sound between a 4k and 20k player, but net worth millionaires as a group wouldn't care - they would state that even a 4k player is too expensive for what is obtained from it. It's something they don't need. It's one of the reasons they became wealthy.

Ausjoe brings up an interesting thought; modded cd players. I at one time tried the Ah! Njoe Tjoeb 4000 (highly modded Marantz turned into tube cd player) and thought it very nifty. I had read much about it, and about the fact that it was supposed to outperform $3k units.
I found a stock Rega Planet 2000 to be superior, to my ears. It seemed that the modding of the Ah! did not produce such a superior player. Sometimes it seems all the modding is similar to taking an economical car, such as a Honda CRX, and putting $15,000 of mods on it. It may stand out, but it's not truly a classy car (I'll add IMHO, lest I offend someone who feels such mods make a car classy).
Sometimes I wonder if the modded cd players, amps, etc. get noticed, but a quality, higher priced production unit will produce a more pleasing presentation. With some frustration, I've learned the only way to truly know is to purchase the contender and compare it side by side to the reigning champ.
However, having gone through the modded test once and ending up with a stock player, I'm in no hurry to go that route again. I'd probably look to a higher level of stock player which has garnished positive reviews from professional reviewers as well as enthusiasts.