At the tender age (OK, ripe old) of 66, I got my first pair of glasses (reading) a couple of years ago.
Since I was 12, I have been on the water almost constantly and have always purchased high quality, reasonably expensive sunglasses. As prices soared on what I was using, I'd switch to another brand, but always quality glass lenses.
I have never had a cataract like so many of my boating peers, nor sunburned eyes.
With Vuarnet sunglasses passing $450.00 a pair (which I'm presently using and purchased for $160.00), I am now on the hunt for another brand. It's so difficult in these days of designer sunglasses to find a really good quality lens that actually protects one's eyes from the reflection off the water, as well as normal sunlight.
I agree, $450.00 a pair is an obscene amount of money to spend on glasses, but at around $150.00 for 5 or 6 years of quality, I'll spend the money. They always go in a hard case (one mounted by the companionway and the other on my belt when going ashore) so they don't get scratched lying around, and using the little rings that go between the frames and arms to keep them tight on my head, I don't lose them overboard any more.
The point is, how important is your eyesight to you? Do you want to bet your future eyesight on a pair of drugstore cheapos?