I recently bought a pair of Performance Bike sunglasses...the style is called Athena. They were $29 and came with three sets of interchangeable lenses. So far, I'm very happy with them. They seem a little flimsy but I wasn't expecting too much at that price. They are very lightweight and comfy though.

I wear contacts and my eyes were watering and tearing up like crazy with my old sunglasses. I had tears pouring down my face within 5 miles! But today, with these new sunglasses, I hit a new personal speed record (41.5 mph) and I had no teary eyes whatsoever!