I don't remember Rosewill ever using Costar at all. CMStorm is definitely Costar. They only have a slight difference in their PCBs and the mini USB type B connector on the QuickFire Rapid. The connector for the USB cable on the PCB is identical too.
Not as much as buying one but it will take a fairly long time.
I'm not into building my own. Check Geekhack or Deskthority. You'll need soldering skills, a lot of green switches(which are different to every other MX switch due to plunger design) and a black keyboard(or one you don't mind tearing all the switches off first).
EDIT: You could make "ghetto greens" by replacing all the spring in your blues with black springs.
Eh...I think actual MX green switches have an actuation force below of those of Blacks by 5g. I don't remember. I'm going to have to go check the Deskthority wiki, which reminds me, I haven't been on the forum over there in awhile.
Why the carbon fiber?
And also, although it may be less expensive, it's a crapload of work which IMO isn't really worth the time. You also have to spend the money on soldering equipment if you don't have any like me.
I thought so too.
Someone will replace them soon enough...soon enough...