Personally, I think the answer is very dependent upon the itnended use
If you want it for basic Internet and maybe word processing, then the PC is a lot cheaper, especially if you go the open source software route it's damn cheap. But if they're one of those who want proprietary software and want good software that does everything that you can do on a Mac, then a Mac desktop is cheaper than buying a PC with Windows and loading it up with all the extra software apps that a Mac has as the big jump in cost is the extra fancy software that comes standard on the Mac. If going the lots of software route another advantage the Mac has is it's less likely to need a rebuild and if it does it's a damn sight easier and quicker to do than a Windows system with all those apps.
Personally, I use a PC with Linux (Zorin OS 5 Premium set up with the Win Classic interface), Fire Fox, Thunderbird, Libre Office, VLC, and Gimp on a four year old system that outperforms my son's i7 with Win 7 Enterprise that has double the RAM I have. The apps I mentioned above are all I need, so I'm happy. I save a lot by not going MS Windows and a lot more by not going Mac, but I've re4commended by Windows and Macs to people based on what they want them for and the software they want.
