materials from a reputable supplier cost the same when buying a hundred feet or a few thousand feet . If your buying direct from a mill then the price will be reduced with the more you buy to a certain level , but , mill direct requires minimum order amount which is quite high . A shop that carries a regular high volume of stock may benefit by paying attention to the commodity prices and purchase accordingly

Higher cost savings would be better found in castings , forgings , and custom extrusions , all starting with a high initial material cost which pays off with reduced machine times and waste . This mostly applies to high volume production .
Materials are generally chosen based on their physical properties and how they apply to the application the parts are being made for . This is usually an engineering department decision which is often ignorant of how the parts are processed . It is very often that machinability isn't a consideration . It becomes a possibility when the manufacturing section proposes a free machining alternative which will provide similar properties to the chosen material for the job . This is either shot down immediately by the engineering dept or requires weeks if not months of research and testing by the engineering dept . Time is money and the people at their desks know more than the shop floor , so shot down is the most common occurrence