Expensive teas or...
The cost of the tea depends much upon where and how it is grown and the process after wards the plucking is over.
The tea taste and flavor depends upon the sub species of the bush Camellia sinensis that the leaf comes from. Some sub species are renowned for their quality and are generally sold as premium teas.
The region where tea comes from is also responsible. Like tea leaf from the Darjeeling district in Indian state of West Bengal is highly aromatic and superior in taste and flavor to most of the tea growing regions. Some variety of teas from Darjeeling are highly expensive being more popular in English Tea Rooms. The elevation of the tea grwoing regions also help grow premium varieties of tea leaf.
The weather and annual climate also plays a key role. Other factors are the age of tea bush and the selection of leaves that are plucked for the blend.
The methodology used by tea estates for plucking, rolling, twisting and cutting the tea leaf also plays an important role.
The oxidation process gives rise to green, black and white tea leaves. The green tea leaf is less oxidized than black tea hence retains beneficial enzymes and antioxidants more than the black tea. The white tea though not so much popular is grown in total shade devoid of sunlight, hence the name white tea as it contains less pigments. The tea leaves which we use to brew the hot cup of tea is usually a master blend of many varieties of tea leaf. The better the blending the better the taste and flavor.