How much time to research the whole process? How much time to research the parts required? How much time to decide which parts you want? How much time to buy each component? How much time to put it together? How much time to bootleg OS X and modify it to make it work? How much time to troubleshoot?
That is the most appealing part of it, for people doing it in the first place!! And if you're an experienced builder the troubleshooting part does not take long, if at all.
My hat's off to the O.P. Great job. Of course if he wanted to go full-tilt he could've gotten a Mac Pro case from somewhere, but that would've affected the final price.