Installing carpet on stairs will almost always demand an additional charge. Depending on the type of stairs you have it may cost anywhere from $3 for each standard box step to as much as $15 per step for a double-wrapped stair with a pattern match Berber.nstalling carpet on stairs will almost always demand an additional charge. Depending on the type of stairs you have it may cost anywhere from $3 for each standard box step to as much as $15 per step for a double-wrapped stair with a pattern match Berber.