The lowest prices for parts are most often found in discount stores or the auto department of mass merchandisers, such as K-Mart, Sears, and Wal-Mart. Parts sold here are name and private brand parts bought in huge quantities, so they can offer a competitive price. Private brand parts are made by major manufacturers and sold to large chains under a store label.
You have to have a good idea of what you're looking for when you buy from these outlets. Many are self-serve, in direct contrast to the older, traditional jobbers where they still look up the part number and get the part for you.