In my own opinion, I don't think it is worth buying expensive sunglasses for the students for the following reasons. First of all, buying the sunglasses of brand may grow the sense of vanity for the students which are not practical. Secondly, the students are in the fast growing period which means that the size of sunglasses may be not suitable for the students after a year or two years. Thus, just buying the sunglasses with good quality for the students is OK.
Generally speaking, it counts on what you want out of them. According to the price, you can see the definitely difference in quality and comfort. Especially for the students, their eyes are easily to be hurt, and when you buy a pair of expensive sunglasses, you pay for quality, comfort and reassurance, so as long as you're not one of those people who are always losing things, it's worth it. Besides, if you bought a pair of expensive sunglasses, they will last longer. For instance, if you spend $100 for a pair of sunglasses, they will last for one year, while, if the sunglasses cost you $30, I think they will not last so long, then you will spend more on buying another good one.
To tell you the truth, I myself, when I was a senior high school student, I was really into some famous brands, but now, I see little value inside them because as students, you are not financially independent, you rely on your parents and friends. So, don't you think it foolish to go after those you cannot afford at present? Maybe a few years later, you will be more mature and can buy what you want because you can buy and no one dares to deny that.