Why is the truffle not a cheap product?

Experts divide the truffles into three classes: culinary valuable, culinary justifiable and culinary worthless. Only the white Piedmont or Alba truffle (Tuber magnatum) and the Perigord truffle (Tuber melanosporum), i.e. the “black diamonds” from Italy or France, belong to the top group and are correspondingly expensive: the black ones cost 800 to 2,000 euros depending on the harvest the kilo, the white three to fourfold.