Earlier quoted context omitted.
Off the top of my head (and so, perhaps wrong), I seem to recall the amount Apple is charging for going from 8 GB to 16 GB to be on the order of US$200. [1] For RAM that they are purchasing and installing in volume. That's a lot of net profit into their pocket, for each unit. And that's where I have one particular concern: Apple closing down and engorging itself on yet another market segment (upgrades). You can argue…
So $424 extra for the bigger drive, and $176 for the extra ram... that sounds almost reasonable.
I'm seeing 4 GB DDR3 DIMM's at around $23, while 8 GB DIMM prices -- a bit scant in quantity -- appear to average in the low $50's.
So, say $46 versus $110, for a $64 difference? Very approximately. And I didn't look closely at bus speeds -- just very off-the-cuff.