Check out people like these first.
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Could be more repair than replacement of parts. The lock on the car obviously isnt working bacuase the dent from your door is blocking its path. Once the door is fixed, i'd say, job done.
Even if you have to replace the door (doubt it though), regardless of colour it will have to be resprayed as the original colour of your car like anyone elses, fades over time and will have to be made to match.
Again as PPosters have said, get estimates from at least 4 garages. You'd be very surprised to learn the difference in price range from one to the other hoever, the prices you've mentioned so far are in my opinion, way off the mark. try throw up some images so we can have a look.