APU inside the xbox one X is 360,4mm^2 (wider memory bus + more CU's = bigger chip)
The one inside the PS5 is rumored to be under 300mm^2.
PS5 also uses cheaper ram (they dont have to run as fast, so they can probably get away with a cheaper chip of memory)
PS5 cooling will without a doubt be more expensive, though probably not hugely so.
(the upside is I think, this also means a less noisy & more cool running chip, I expect it to use less power than the series X)
PSU = I expect the series X one to be slightly bigger and thus probably abit more costly.
The big thing against the PS5 is the controller (10-15$ more in parts?).
I expect Sony to have spendt abit more on this part than the xbox's.
SSD = sony spent abit more on it than Xbox, but thanks to it being 825GB instead of 1TB, I suspect its not by a large factor.
I still think overall the PS5 probably be slightly cheaper in to manufacture overall than the series X.
Necro-bump this 2020: http://gamrconnect.vgchartz.com/thread.php?id=229249
Bumb in 2021: http://gamrconnect.vgchartz.com/post.php?id=9047071