So after doing a little research, I came up with a price comparison for this machine, which I have here. Missing from this list are parts for the case alone (which would more likely than not be custom parts), components I plan to transfer between machines, and a few key components and accessories: TV, Amplifier, iPod Touch, Blu-Ray Player, Surge Protector/battery backup, Speakers, and connectors/plugs.
* Denotes where Newegg.com listed rebates - Prices are before adding in the rebates.
First, a huge note: I tried to get parts that were either listed as Mac-Friendly on these sites, or in the case of the hackintosh builds, were listed or proven in a couple of online forums as compatible. As always, parts can change, and as a result prices.
Second, I did not include operating system costs. In both cases this is an upgrade; however, in the case of Intel-built, I could add an extra Thumb Drive and Windows for a dual-boot machine (or to use Windows in a Virtual Box.) If I were to stick with the Mac, I'd be looking for OS 10.5, aka Leopard, since Snow Leopard, aka 10.6, has no support, official or otherwise, with my machine currently. (Good luck finding it for less than $200 - the cheapest I saw was on Amazon.com for $211.00. Snow Leopard is not only easier to find, it's much cheaper as well.)
Finally, I could have made the PC Parts more expensive, just as I could have added more to the Mac side, easily. There's only one thing that can not be fixed, however: The cost-to-performance ratio. Everything on the PC side outpaces the Mac Side by significant numbers, which will result in fast RIPS, more reliable DVR functionality, and certainly more machines it will be capable to emulate. As much as I want to argue with common sense, it would be far cheaper to start from scratch than it will be to upgrade.
It's worth noting, though, that the upgrading with Mac Parts has one key advantage over the build-from-scratch PC Parts: there will be little-to-no hacks necessary to complete this. The counter argument, however, comes from the software side.