Because glasses are so expensive, maybe you could use an online service like http://www.zennioptical.com/ ?

I haven't tried them myself, but I'm going to order some RX sunglasses from them. I have a hard time wearing the astigmatism contact lenses, and I need my sun protection! anyway, I've read good things about that particular site. Even if you still have to pay for the exam out of pocket, at least the glasses won't set you back quite so much.