I visited a small number of opticians to price getting my normal top end lenses put into my old frames. Everyone had the same price, none in writing. I might be suspicious of retail price maintenance but that evidence! None recorded.
Costco was having an optical sale so I figured why not. $300 for a pair of Costco 'Kirkland' house branded progressive lenses made by Eisslor put into my old frames, all the bells and whistles included. Costco was up front about how their product differed from my top enders, and claimed that with my correction I should not notice much if any difference.
Putting them on they were a bit different, but every new prescription has been. Bottom line after a day, $300 out of pocket instead of close to $800, I am totally happy with the product and almost $500 better off.
Anecdotally I might have been over-buying for many years. YMMV.