I bought my last pair at Costco for $25. Costco-brand aviators, looked like designer brands. Wore them for about two years until they broke. I also go through a lot of them, usually misplacing them, a trait I got from my late mother. For about two years after she died, pairs of her sunglasses would pop up around the house, in the cars, etc. We always took it as a sign she was thinking of us.
Funny thing is, I've only splurged on sunglasses once -- on a pair of RayBan aviators I bought and thought I lost 10-12 years ago. I've been in major purge mode and recently found them. Thankfully they're back in style.