Here's a cool place that I found. Obviously, you need to get your eye exam and prescription first, but they have single vision glasses starting at $8 complete! I haven't gotten glasses there yet because I just found the link. But I got the link from the National Marfan Foundation. They recommended them, because young people with Marfan's have frequent changes in vision and that gets really expensive.
http://www.zennioptical.com/cart/home.php
http://www.zennioptical.com/cart/home.php