You can build something with those specs at a cheaper cost right?
With those exact specs you're looking at spending a bit less, but not by much. Truth is, most people who build workstations don't go for the absolute craziest specs. 64GB of ram, dual GDDR5 Graphics cards, and 12 cores at 30MB of L3 is crazy power but I can't see use for going all out in that sense. At around 8K that can all be had on a PC workstation, while it's hovering close to 13k on the Mac Pro. Regardless, I'm typing this up on my Macbook Pro because I felt that the SSD drive ran way too smoothly on iOS to choose a PC laptop.
The flash storage on the Mac Pro should be incredible though. I will definitely try to opt into some flash storage the next rig I build.