Expensive fungi, such as truffles, are a type of mushroom that grows underground and is highly sought after for its unique flavor. Truffles are one of the most expensive types of fungi, with prices ranging from hundreds to thousands of dollars per pound. They are typically found in the wild and harvested by specially trained pigs or dogs. Truffles are used in many dishes, from pasta to desserts, and are considered a delicacy in many parts of the world.