I don't actually think the XBox Series X will me much cheaper either, they'll just launch a cheaper version that will actually compete with the PS4 Pro.... but they'll convince people it's a next gen console...
I don't think people understand how much a SSD with a readspeed of 5.5GB alone costs, total cost of the system must be pushing 1000 USD already.
Sony are buying cheap nand chips for use in the PS5, using custom hardware to eliminate all bottlenecks in the I/O and using 12 DMA channels. They can reach the theoretical peak speeds much better compared to a PC part. I.e If you could connect Sonys SSD nands on your computer, it would probably perform worse than many PC offerings. The same could be said the other way around, where a mid-tier ssd stick for the PC would perform much, much better once connected to the PS5's i/o
So it's not the chips itself, its the combination with specialized hardware that makes it tick. No extra licence costs either since it's their own tech.
I think they were aiming for $399, but with the current global landscape atm I'm guessing $449 and the Series X at $499/$549
Because of their more expensive APU (size)