i want to buy a bike commuter bike, but the expensive commuter bikes had disc brakes and not the cheaper ones. so How much would it cost to add disc brakes onto a bicycle?
Your frame and wheels need to be the type for disc brakes, period.
See Edward - the pot calling the kettle black? In caps lock screaming about department store bikes while touting his employment at the "junk store". Go to a local bike shop not the big box bike shop.