Polycarbonate ones don't shatter. And when you sit on or loose em they better be the el cheapos.
Get to MArshalls if you want to score a pair of $50-70 Bolle's for about $20. I posted this on the other board. You won't miss any fish either with the cheaper varietites. The exception might be if you're a flats hound. Then the investment is worth it. OR if you're careful enough to take care of a nice pair. Not me.