I've gotten a few pairs from Zenni. They're pretty good, not as high quality or long lasting as what you'd get for $300 at a regular US store, but at least 60% to 80% of the way there for $10 to $60. Some of the plastic frames cracked, and one lens had a weird faint line on it.
Make sure you get your pupil distance (PD) measured on your prescription, some eye doctors don't write that down. It's also a good idea to get measurements from a pair that fits you well, and order something close to the same size.
I don't know if they still sell that little camera lens looking gadget that's supposed to allow you to do your own eye exam, but it's a waste of money and doesn't work.
