you must be dreaming if you believe the ps5 will be 399, that ssd alone is worth at least 150 dollars.
In reality, there are 12 low-cost chips that make almost the entirety of the ssd (at 5.5GB/s, this is way below the "doable" transfer rate with fast, hot chips). The real cost is in the custom controler but that goes under R&D as it sits inside the SoC. So I'd guess around $40-$45 for the 768GB ssd.
My guess would be $50 off for the no-disc version, so either 499/449, or 549/499 if they don't want to lose money on hardware.