The rotors (sometimes called discs) are the parts that the brake pads clamp against to brake. Rotors are in the $40-$50 US price range. If you are having vibration braking at speed or even down toward low speed then the rotors are most probably the cause. Another issue with our cars is the upper control arm bushings failing and this manifests itself as a vibration when driving (not braking) at speeds in the 60 MPH and up range. The job of replacing the rotors is quite easy if you have any mechanical ability.