I got some astoundingly cheap (like $11 shipped) wireframe glasses from Zenni, an outstanding bargain. I then got some $38 prescription sunglasses from Zenni, but was disappointed in their quality (lenses weren't seated evenly). I also got some $19 frames with fancy Transitions lenses from EyeBuyDirect, and was really pleased. Those are my daily glasses.
I think frame and build quality is a bit of a crapshoot, but the prescription has always been perfect.