Could someone speak to the RAM installation and the materials cost involved in the RAM upgrade? Would it be akin to going from two 4 GB "sticks" to two 8 GB sticks?

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.

That's exactly right. The memory interconnect on the board is the same as it is anywhere (the DRAM controller in modern Intel CPUs is inside the chip, so the memory is just directly connected). The only difference is that the chips are soldered to the board instead of being on removable DIMMs.