Just ten bucks? Where can you find that kind of sunglasses? On the streets or online? I think a pair of cheap sunglasses will cost us at least $50 if they are just a pair of regular sunglasses. And a pair of polarized prescription sunglasses will cost us more than $100 dollars. Maybe the sunglasses that only charge for ten bucks are of poor quality. I will not suggest you to buy that kind of sunglasses because they can't protect your eyes from the sun.
Compare a pair of famous brand sunglasses with a pair of common sunglasses, which one do you like best? Of course the famous brand sunglasses are more expensive. But if we don't take the price into consideration, we may definitely choose the famous brand sunglasses because the quality is better and they are also of the latest fashion. They are more elegant to some degree. So of course they will be more expensive.