3d print aluminum valve cover for car
This is a very large part. My estimate for the cost would be a few thousand to get this printed in metal, if not tens of thousands (assuming it even fits the maximum build volume of the printer, which is only 440mm on its longest axis).

3D scanning also isn't a very reliable way to reproduce parts, especially for something mechanical that needs to be precise. You can not just scan something and then print it like making a photocopy. A lot of manual design and reverse engineering work would be involved.