if they can make the cost cheaper than what someone would spend buying a pre-built PC
It's Razer so I doubt it.
Not just because of this, but it adds quite a lot of casing to each component, which needs to be designed, manufactured and assembled.
I think normal pre built computers will be cheaper.
And when I describe to people what building a computer from scratch means then I use the lego metaphor all the time, it
is already that easy. If you are able to use Wikipedia then you can build a computer. The first time will take some time because you need to look up everything (DDR(1|2|3), PCI, SATA, LGA<bla>, DIMM, etc.) but I don't think you need any previous knowledge.
It's like building something with Lego according to a manual. I did this often as a kid, first building some kind of modules from the actual Lego bricks and then assembling the modules to, say, a monster track with a working gear box, steering wheel, etc. (that thing still is somewhere around here
. It's even easier with PCs because those "modules" always connect in the same way and you only need to look it up in the manual once.