Hello; Early bus manufacturing grew out of carriage coach building, and later out of automobile or truck manufacturers. Early buses were merely a bus body fitted to a truck chassis. This body+chassis approach has continued with modern specialist manufacturers, although there also exist integral designs such as the Leyland National where the two are practically inseparable. Specialist builders also exist and concentrate on building buses for special uses or modifying standard buses into specialised products. Integral designs have the advantages that they have been well-tested for strength and stability, and also are off-the-shelf. However, two incentives cause use of the chassis+body model. First, it allows the buyer and manufacturer both to shop for the best deal for their needs, rather than having to settle on one fixed design-the buyer can choose the body and the chassis separately. Second, over the lifetime of a vehicle, it will likely get minor damage now and again, and being able easily to replace a body panel or window etc. can vastly increase its service life and save the cost and inconvenience of removing it from service. As with the rest of the automotive industry, into the 20th century, bus manufacturing increasingly became globalized, with manufacturers producing buses far from their intended market to exploit labour and material cost advantages. As with the cars, new models are often exhibited by manufacturers at prestigious industry shows to gain new orders. A typical city bus costs almost US$450,000.