Genuine musk is hardly existent anymore and thus extremely expensive. I believe only very few natural perfumers actually use it, and perhaps some bespoke perfumers in the Arab/Asian world. Most of it is probably wasted on ancient "natural viagra" formulas.
To the excellent comments by pluran and the_good_life, I'd add genuine ambergris (from whales) and high-grade jasmine.
Oakmoss and high-grade sandalwood will be scarce in the future, and therefore those prices will rise. And oakmoss is facing health restrictions in its usage, as well.
Aged Mysore Sandalwood
real Agarwood (black) from old trees
All of these are quite pricey, and anything certified organic is about double the price.
BTW, does anyone know why Melissa is totally banned by the IFRA? I looked on their website and there was no reason listed.