You can buy $5 sunglasses at Walmart, or $100 sunglasses at a Sunglass Hut or the like, or even up from there; and they seem to do the same thing. Given that, and given that I often scratch or break my sunglasses within a few months, sit on them by accident, drop them, lose them... I have always bought the cheap sunglasses.
And I've always been mildly dissatisfied. They're always a little scratched, they always get smudged too quickly, they always bend a little or don't fit right, they always have a nick or crack. But I can just get another pair.
I've tried $20 sunglasses and they haven't really changed that. Sometimes they fit better, look better, even work better, but they don't last longer. I'm just as hard on them as on the cheaper ones. Last year I tried some $30 glasses from a touristy shop in Ogunquit that might have been higher-end than their price indicates (or might not); they looked great, felt pretty good (though they weren't dark enough for really bright sunlight), fit good, and died after about six months, a fairly typical lifespan for the $5 glasses for me.
I wonder whether the $100 ones (or higher) would really work better for me. Maybe glasses made of glass with scratch-resistant coating, with a well-built frame that can be maintained and repaired, and a good case, would not only work better for me but last long enough to justify the price. I would love to have a way to find out that wasn't "buy some, and then maybe drop them a month later and feel like a fool for wasting that much money".
I've read many accounts of other people who made the move from $5 to $100 glasses and swore by them afterwards, wondered at how they'd ever tolerated the cheapies as long as they did.
And if you think about it... people who wear prescription glasses almost always manage to hang onto them for years without major breakage, scuffing, scratching, or losing them, especially if they get scratch-resistant lenses. Maybe I could too? Then again, those people wear their glasses most of the day, so maybe that makes it easier to not lose them than if you had to have sunglasses around in case you needed them, but not actually wearing them most of the time.
The trouble is you can't rent good sunglasses to find out if you're going to trash them. There's no way to find out but to put your money down and roll the dice. Maybe one day, I will. (Though if I do, there'll be no compromises: it'll have to both look good and feel good.)