The 1800X at $500 was a pittance compared to what Intel was charging for more than 4 cores at the time. Being able to have 8 cores without needed a more expensive HEDT board on top of the much lower price compared to the competition meant that it was a great value even at $500.
Even the $330 1700 was able to hang with Intel's 8-core HEDT offering in some benchmarks. One third the price, half the power, same performance.
Zen completely changed the market. So much so that what ~$500 should get you for a CPU also changed, significantly. The $450 that the 5800X launched at wasn't considered a good value which is why it was the one that was pretty much always in stock. It was better value for money to either pay $150 less for a 5600X that was just as good for gamers or most other users or an extra $100 to step up to the 5900X which gave you an additional 4 cores and would easily win in any applications that could leverage them.
I think the 5800X3D can justify its $450 price tag, and it seems like consumers generally agree since it's nowhere near as easy to get as a 5800X was when it first launched.