Progressive lenses require taking a measurement from the center of your pupil to the bottom of the deepest part of the lens. No on line company can do this accurately. You also need other measurements, and if not taken without the frame on your face what do you think the chances are it comes out right? (Full disclosure I am a license optician in CT for over 20 years) There are over 100 types of progressive lenses. Some came out in the 90's and some came out last week, there is a big difference how they work. Take a computer from 2000 and compare it to one today. On line or Costco you get the 2000 version of progressives. Most on line or Costco type place glasses offer no warranty on a product not designed to hold up as well. When you go to a private practice you pay for service, expertise, quality and that they will stand behind it. There are some ways to save money but remember you will use theses every day for a couple of years. I bet if you could only wear one shirt for the next 2 years it would be made well.