On the left are my tried and true Oliver Peoples sunglasses; the one you've seen on this blog probably far too much. On the right is a pair of free sunglasses that I think I got from a swag day at my company. They look similar, but let me tell you why I think it's worth it to go with the sunglasses on the left over the ones on the right.
Okay, I'm going to throw a little bit of a curveball at you. Instead of focusing on style, quality, longevity, durability, and other very important benefits to having premium sunglasses, I'm going to focus instead on a reason that people often overlook when deciding between crappy sunglasses, and a pair of, let's say, Ray-Bans.
Generally when you pay the extra buck or two for sunglasses, and this doesn't have to be some outrageous amount (like $450 for Prada glasses), you will end up caring about your sunglasses exponentially more than if they were some cheap $15 glasses you found at a flea market in Brooklyn.
Before I started spending more than $25 for a pair of sunglasses, I probably replaced about 20-30 pairs, and each had a maximum lifespan of about 5-6 months. I may have left them on a table somewhere, or accidentally crushed them in my pocket, but in either case, I didn't really pay attention to the glasses because they were so cheap and replaceable.
Then I bought a pair of Ray-Ban wayfarers on sale for $75. The moment I got those, not only did the glasses look and feel much better than my previous pairs, but I also cared about them far more. I took care of them when I could, I made 100% sure not to lose them or put them in some compromising situation, and also incorporated them into my outfits much more thoughtfully. I would assume this all happened because psychologically, I just couldn't accept losing a pair of $75 Ray-Bans due to some in-the-moment stupidity on my part.
So my recommendation is to try a nice pair of sunglasses out sometime if you don't already own a pair. You'll find that the fear you have about losing them or crushing them and wasting your money will actually help you do just the opposite.