Apple won't port to the PC hardware platform (actualy, they are both PCs, but that is a different matter). To do so is just a really bad idea. Everything just works with a Mac because you have the same person controling the hardware and software. As soon as you throw Mac OS out there with completely different architectures it would only invite many of the same problems Windows has over to a new home.
Apple hardware costs more because its better. That said, you can get comparable hardware for PCs, but its the nicer stuff. You would wind up paying about the same ammount anyway.
And before anyone compares cost per GHz, PowerPC processors are more efficient than offerings from AMD, which are more efficient than offerings from Intell (typically). G3,4,5 processors match performance of faster Pentium n class processors at lower clock speeds.