Just to paint the exterior of the door will probably run you around $300. It will not match perfectly without "blending" the adjacent body panels as well though. Your car has a metallic color and metallics are sensative to air pressure, humidity and the angle of which they are sprayed. You can spray 3 panels on your car on three different days from the exact same batch of paint and you will have 3 different shades of blue just due to atmospheric changes. To do it properly will probably cost you around $800-$1000