Zenni is pretty cheap. I've broken several pairs, but at $8 you can kind of afford to throw them away. The frames are usually midgrade plastic. I usually order 3 or 4 pairs at a time, assuming I'm going to lose or break at least 2 pairs.

But despite the quality, theres some pretty stylish options that are perfect for people with no optical insurance :D

Also worth noting, the shipping time on Zenni takes forever. Forever being at least a couple weeks in my experience, but in fairness I haven't ordered recently.