I am not speaking to the legitimacy of this, but I don't recall seeing this on here.
$300 would be the right price for Lockhart / Series S, as any higher than that would make it a terrible value, if PS5/XSX are $500.
However, if Sony manages to sell PS5 at $400, then Series X is going to look bad even at $300. I don't think PS5 will be $400 though, I think it'll be $500.