And of course he's 100% right - but he's answering the question "what's the difference between copper necks and brass necks?" not "do you pay more for them wholesale?" which I happen to know he does because I worked with him and we shared our pricing information. Copper necks cost Phil (or anyone else) more to to manufacture than brass necks and silver necks cost more than that
Dollar for dollar perhaps the most expensive necks to make are the wooden ones eg by Paraschos - they must take a LOT of skilled work to perfect and at the end of the day it's the hours of skilled work taken that will push the prices up more than the material used (unless you make them out of solid gold or platinum or something and encrust them with emeralds and rubies of course - that would make a very tasteful and understated neck!).
The wooden necks are a work of art I reckon, though again the material itself will not predicate a different tone. That said the difference in side wall thickness of a neck may make a difference - it's something I keep meaning to research.