You could certainly make a case that the 1800X was overpriced, but when it came out the competition on desktop was a quad-core (7700K) released 2 months earlier at $340. You also had the 1700X at $400 and the 1700 at $330. When the 9900K launched, you had the 2700X launched 6 months earlier at $330. It was a big jump to HEDT when the 1800X was released with the 6900K over $1000 while the 2920X was $650 when the 9900K was released (and the 1920X selling for $420-$430).
The 9900K keeps getting compared to the 2700X because they are both 8C/16T chips when in reality it is 20 - 30% faster overall and is a clear tier above in performance - the 9900K actually compares better to HEDT chips like the 7900X and 1920X than the 2700X (see the aggregate scores in 3 seperate reviews:
TPU +20%,
Computerbase +22%,
PC Gamer +30% )
In reality the 2700X is a competitor to the 8700K/9700K as shown by the links above, and is priced accordingly. The 9900K is $500 because there is actually no competition from AMD in this price segment (apart from the HEDT chips).
Anyway, my point was that $500 in a desktop CPU is more common than people will care to admit, from both Intel and AMD. I used the 1800X because that was the most recent example before the 9900K, but going back there have been many chips at $500 or even $1000 in the desktop market. Do people remember the Athlon FX or Pentium Extreme Editions?
Back then there wasn't a 'HEDT' segment, so the $500 - $1000 CPUs were lumped into the same category. Nowadays, we have Skylake X and Threadripper for those pricepoints, but the 9900K somewhat blurs that line because it offers entry level HEDT performance on a desktop platform.