Underneath the sheetmetal, the Charger is essentially identical to the 300 and Magnum so there is significant cost savings by using all of the existing tooling, jigs, and various other components. A new chassis would have to be engineered, tested, and then adapted to the assembly line, or a special line would have to be created. If the Challenger is to be the first of the LY platform (more flexible than the LX, i.e. wheelbase, doors, transmission type), then these added costs are more of an investment for the new cars coming down the road. But on its own, a car with these changes would cost more than what went into the Charger.