We get a lot of questions about replacing lenses in non-prescription sunglasses. LensFactory can replace lenses in non-prescription sunglasses, but it is usually prohibitively expensive. For instance, we have to use "plano" blanks which cost us just as much as the prescription blanks and the tinting and edging process is exactly the same as with prescription lenses. So non-prescription sunglasses can be re-lensed with tinted single vision lenses using plano blanks.
If the sunglasses are what we call "wraps" where the lenses curve steeply around the side of your head, it gets even more expensive. We have to use tinted freeform which are custom machined using a $300,000 freeform generator.
I wish we could do non-prescription sunglasses for less. They just aren't really designed with the replacement lens process in mind, so we have to use prescription lens materials and techniques which usually cost more than people are willing to spend.