When you build your own there is no labour cost at all - just try costing out your own time by the hour and see how that changes the figure of the home-built one.
Exactly, and most of us don't realize the value of our own time because it's our own time. When we apply our time to "A" we're taking it away from "B" because there is only so much time in the day. If one has a lot of responsiblity (work, home, parent) then they have even less time to apply to various things and that available time is even more valuable.
This applies whether were are good at something or not.
For example, I enjoy working on cars. When my truck decided to rust out in the wheel well areas I took it to a body shop for an estimate - $500 per side to repair and paint. "Fuck that" I said, and bought the repair panels for $80 each with shipping, took the bed off my truck and put it on sawhorses, then spent about 100 manhours cutting, welding, grinding, sanding, filling, sanding, more sanding, finally primer and paint. It looks fantastic. But, with all the distractions I have in my life (house, work, family, kid, other hobbies) that's 100 hours of my life I won't get back. I enjoyed the project immensely, I like this stuff, but in the end if I paid myself the body shop's quote of $1000, minus materials (panels, body filler, primer, paint, welding wire, electricity for welder), I "got paid" about $2.50 an hour.
Would you work for $2.50 an hour? Probably not, considering minimum wage is far higher than that ;-)
So there are a lot of ways of looking at things and for someone who is not computer savvy by circumstance or choice, buying something for a bit more money is just easier.
After all, as we bickered on this thread, the OP probably already used his pre-built computer to record something. ;-)