Which of these four types of cheese is the most expensive?

Pule cheese or 'magareći sir', is a Serbian donkey cheese made from 60% of donkey milk of Balkan donkeys and 40% of goat milk. Pule is produced at the 'Zasavica Nature Reserve' in Serbia.

Donkey milk doesn’t have enough casein to make cheese, so it is combined with goat milk. The flavour is unique, sweet, clean and mild.

A distinctive dairy product of Serbian cuisine, pule is reportedly the "world's most expensive cheese", fetching 1,000 Euros per kilogram ($600 per lb). It is so expensive because of its rarity; there are only about 100 jennies in the landrace of Balkan donkeys that are milked for pule-making and it takes 25 litres (6.6 gallons) of milk to create one kilogram (2.2 pounds) of cheese.

Currently the cheese is made only on advanced order basis but farm exports are expected soon in the United Kingdom, Germany and the rest of the world.

Rich in vitamins and minerals, donkey milk is believed to slow down the ageing process and has been used as an immunity booster in the Balkans since ancient times. Cleopatra allegedly bathed in it this milk. It is also purported to boost virility. Regardless of the legends, at $600 per lb, it is a very nice treat to savor and enjoy.