You might not like it but opticion business is the one you are looking for (glasses/sunglasses shop)
Cost of materials is very low. Inventory of less then 3 to 4 lakhs can fill a whole shop. Not a very big shop needed. Machines are small and not expensive at all. Only a very small workshop sort of thing is needed behind ur main shop for making the glasses. 4 ft x 4 ft should be enough.
Go to Lahore Shah aalmi market and check prices of frames there. They start as low as 20 rs and the really good ones are for 300 to 400 or so and these are the ones that are sold for like 2000 rs or so. Same for lenses. All you need is a location where there is a lot of foot traffic, hire a salesman and a technician and you re ready to operate!
You might never become a multi millionaire from one shop but the ROI is very high, that's what you asked for...