To buy an RTX 4090 of the same or similar model is double and more. There is no way inflation, R and D, and wafer costs justify why a GPU should cost that much. You can buy a top tier motherboard, DDR5 6000 RAM and 7000 series CPU, all combined, for half the price, or less. It makes no sense...
First off you can 'justify' any items purchase price based on if its offering something that no other competing product can do at that given moment. Elements of a Formula 1 car, the latest smart phone, clothes fashion.
A motherboard, high design cost chip and memory mixed with the R&D is precisely what the 4090 is, so the comparison with an intel build computer is very apt. Apart from your example is 1 cycle behind. Intel's manufacturing node just isn't quite as good. The DDR5 memory isn't as fast. The Nvidia motherboard isn't as big and maybe not as complex, but you are paying for a huge chunk of precisely machined expensive heavy metal. And the "top end" isn't "half the price" or less. Its exactly the same price as the Nvidia product.
As to the opening poster's complaint about price and power. The 4090's performance at lower power levels was slightly better than I was expecting. I might pick one up 2nd hand eventually to replace my 3090. If he wants a 200W card and its purely for gaming, then I'd suggest he wait to see what AMD have to offer next year. If he wanted supreme value for money, he should have picked up a £300 6700 (nonXT) last month or reference 4060ti when they became recently available again.