It used to be called a "root canal" until the American Association of Endodontists redesignated it "Non-surgical Endodontic Therapy." It is the same thing, same basic process, same materials. Instrumentation, irrigation and filling techniques have changed enough to have alleviated a lot of the "experiences" folks used to have with "root canal" treatment so the specialty decided to give the procedure a new name.
The cost is moderate and depends on the size of the filling and the technique used by the dentist to place it in the prepared tooth. It generally takes longer to place a composite filling than what is required for an amalgam filling. Composite fillings require a cavity that can be kept clean and dry during filling and they are subject to stain and discoloration over time.