I wear glasses mostly to protect my eyes from things thrown up from car wheels and the like. One thing that the fakes are not going to be is polycarbonate (i.e. Lexan). If you ride enough you are going to get hit in the face or and eye, sooner or later. I'm not trying to support the high end sunglass industry, but at least make sure any glasses you get are polycarbonate or sometype of shatterproof material. If you get that, they are bound to do all of the UV protection as well. If you have to go cheap, go to Home Depot or an auto parts store and get safety glasses (great for rainy days!). There are ANSI standards for safety glasses and any decent pair will list this. You can get safety glasses that are tinted for the outdoors.

Are your eyes worth more than $8.95? Think about it.