For years I purchased my eyeglasses locally, and then during a trip to Italy to visit my sister in Rome she introduced me to a friend who owns a eyeglass shop. I purchased eyeglasses from him. I am now aware that when one pays cheap prices here, one is buying cheap lenses (probably made in China). The problem is also that there is no way to tell if a eyeglass store prices you for expenses lenses that they are actually delivering those expensive lenses. Good lenses make a difference. Every three years or so I now have visited my sister to get new lenses.
I suggest you pay the difference and ask for good lenses and ask for a way to verify the lenses used are not cheap ones purchased from China. A good oculist in Santiago will be able to tell you who has the better lenses.