Depending on how much hp, new mounts, fans, fuel system, tank, tranny, rear end, trans cooler, and possibly hood. About 6-10k for 600-650 hp.
Packing in more air allows the engine to add more fuel and therefore creating a bigger explosion inside the cylinder creating more power. The amount of pressure applied to the intake manifold is known as boost pressure. In a standard turbo this pressure is controlled by a waste gate that allows excess pressure to be vented to the atmosphere.