They may be dirt cheap but they are made from a top quality optical polymer with a multi-layer Anti-Reflective Coating cut to your specifications. These are NOT polycarbonate, it has too much distortion. Look through a polariscope at a Polycarbonate lens and the distortion is plainly visible The material I'm using has much better optics. Lenses are sold separately or as a collection of four (2x, 4x, 6x, 8x). The single lenses are $45, the set of four is $140. I have been an optician for 30 years working in the optical field. I have quite a bit of experience dealing with the fabrication of specialty items.