We are not only pay for the materials of sunglasses, but also the whole package of the sunglasses including the design, publicity, and prescription.
For those good sunglasses are always special designed, and the quality can be assured.
You need to know that the manufactures, retailers need to make profits over the sunglasses. If you want to buy some good sunglasses with low price, you can shop online. They cut lots of intermediate costs which can save you lots of money.
Good sunglasses are expensive due to the following reasons. First, expensive sunglasses always have a nice design, they look wonderful, so the design is quite cost. Second, expensive sunglasses are also good in quality, and it is quite durable. At last, it is related to brand, good brand always gives a pair of sunglasses a high price.