The thing I was going to claim to debunk was that the cost of the Macs vs the cost of PCs would be the same, regardless of what components you used.
Here, let me show you what you'd get for cost if you built a PC with the EXACT SAME processor, the same RAM, (as close to) the same graphics card (the 5770 is ancient, they only have 6770 on newegg anymore), etc etc. I'll even provide you with links to help you follow along with me.
Okay, so. Let's visit Apple.com.
Apple - Mac Pro - View all the technical specifications.
There's the tech specs for the Mac Pro. The processor is "Two 2.4GHz 6-Core Intel Xeon E5645 processors" for the dual CPU model. Newegg offers two of the E5646 for this cost...
Intel Xeon E5645 Westmere-EP 2.4GHz 6 x 256KB L2 Cache 12MB L3 Cache LGA 1366 80W Six-Core Server Processor BX80614E5645 - Newegg.com
$575 for one, two will set us back $1050. Now let's look at the memory. It claims it's using "1333MHz DDR3 ECC SDRAM." Okay, let's get the most expensive 12GB (standard for the Mac Pro) server grade RAM we can on Newegg.
Kingston Server Memory DR x8 Intel Model KVR13R9D8K3/12I - Newegg.com
$112 for that. We're at $1162. Now on to the graphics card. The 5770 is too old to find anything other than refurbished, so let's upgrade to the 6770 1GB model of the ATI Radeon.
VisionTek 900447 Radeon HD 6770 Video Card - Newegg.com
$120, total $1282. Now let's look at hard drives. I know they use Samsung for their SSDs, because my friend runs an IT business and he's had to repair and replace one recently. We'll do the 512GB plus a 1TB 7200.
SAMSUNG MZ-7PD512BW - Newegg.com
Western Digital WD Black WD1002FAEX Internal Hard Drive - Newegg.com
$520 for the SSD, $100 for the HDD, that's $620, so $1902 so far. Now on to the optical drive. Theirs doesn't even support anything but DVDs, I'll go one up and get a Blu-Ray reader so we can watch HD videos if we'd like.
ASUS Model BC-12B1ST/BLK/B/AS Black Blu-ray Drive - Newegg.com
$60, at $1962 so far. The rest is just getting a case, a motherboard, a mouse, keyboard, and monitor. Let's do all that right now.
EVGA Classified SR-2 270-WS-W555-A2 LGA 1366 Intel 5520 SATA 6Gb/s USB 3.0 HPTX Intel Motherboard - Newegg.com
Rosewill BLACKHAWK-ULTRA Gaming Super Tower Computer Case, support up to HPTX, come with Eight Fans,Top HDD docking - Retail - Newegg.com
Logitech G700 Black Mouse - Newegg.com
Logitech K400 (920-003070) Black Keyboard - Newegg.com
After all that, the total cost is $2857. There's also a 27" ASUS monitor for $700 that saves $300 on the apple one, but since you can use either on a Mac, I didn't specify. Another $200 if you want Windows 7 Pro and you're at $3057.
Spec'ing the Mac Pro the same with gets you $50 under $5000, and it has less option for improvement later, more PCIe slots, and even a Blu-ray drive. SAME exact parts taken right from Apple's site, almost $2000 cheaper.
These are the facts. You're wrong.