Sand casting is cheaper than die casting if only 5,000 parts are to be made. Die casting is cheaper than sand casting if more the 50,000 parts are to be made. Sand casting and die casting cost the same if around 9000 parts are to be made. In practice, there will usually be lots of processes to compare, and so there will be a lot of curves to draw.
Manufactured sand or manufactured fine aggregate (MFA) is produced by reducing larger pieces of aggregate into sandsized aggregate particles. Manufactured sands tend to be used in mixtures in areas where natural sand is not available or not cost effective to be hauled to the needed location.