2005 Renault Scenic

Engine Mechanical problem
2005 Renault Scenic Front Wheel Drive Automatic

Have been told there is an alternator problem and it needs replacing is a quote for £600 from a renault dealer reasonable. I have a warranty and would like to check if this is a usual or exhorbitant fee. Also the car was stalling before, usually on starting but kangarooing sometimes when travelling as if it was going to cut out. Would thids have been the cause?