Some ingredients are simply specialties in the region, i.e. the Yubari King melons in Japan. The melons are so highly valued that they're often given in a pair as a gift to employer or host. Some ingredients are limited, like the white truffle, which is grown only in the forests of northern Italy for a short period. Or, the swiftlet nest in China is also limited. The nests, which dissolve in broth to form a "gelatinous" texture, take two months for a male bird to produce.
But more than that, some are just weird: the "civet" coffee is produced from the dung of the civet, a cat-like animal in Asia or Africa. That's right, the coffee beans have passed through the civet's digestive system, fermented in digestive acids, and are said to produce a less bitter coffee. The price? $1 per gram — or a mere $500 per pound. We'll stick with Starbucks, thanks.