Cost to replace the 2nd row seat of the wire harness to start the motor? on 1999 Mercedes-Benz C230

When I turn the key in the ignition, sometimes it will crank but won't start, but always starts on the 2nd or 3rd try. Also, what should it cost to replace the crankshaft position sensor, and the starter? Please respond asap. Thanks

Asked by for the 1999 Mercedes-Benz C230