There are many websites that sell prescription glasses which are very cheap. I know one Firmoo.com which is a good online optical store.They have prescription glasses with high quality yet competitive price. I bought a pair of prescription glasses from them and it works well.
Try Firmoo, it is one of the best places for purchasing glasses online, they have wide selection of frames, wide choice of lenses and competitive price. And what impress me most is their customer service, that was my first time purchasing online, and I am know nothing about it, but the guys are patient and guide me how to place my first order online. Check out at www.firmoo.com