why if change manufacturing of a product not change the price for the buyer?
In highly developed and competitive industries companies tread a continuous and very fine line between maximising shareholder profits by keeping prices up while making products as cheaply as possible, vs competitors lowering prices when they work out a way to make equivalents cheaper. In the short run you will quite often see companies hold onto large portions of efficiency savings (particularly if they make a major breakthrough in a specific manufacturing process etc) by holding old prices up, but in the long run competition pretty quickly lowers prices as the companies trying to keep high margins and prices get ruthlessly undercut by smaller competitors happy to make a bit less.