As a side note, the wholesale pricing of solder also seems to be
heavily volume-driven. A small distributor to hobbyists might buy
a couple of hundred pounds at a time, while a large industrial
distributor buys tens of thousands. They get a huge discount for
that, and can easily pass that savings on to their customers.

But we still don't have an answer to the question of why there is such a
wide disparity in the /relative/ pricing of 60/40 and eutectic solders.