my polarized sunglasses is too dear!

[glasses lens]

I purchased a pair of polarized sunglasses recently, as I need them for driving, but the cost is too dear about $300. And the, my brother told me that he ordered one online with under $100. So cheap! I find these sunglasses are always much more expensive than ordinary eyeglasses, about $200 average, i will choose online store at the next business.
Thank you!