While I do think that 20 bucks seems a bit high, there are some points in this thread for it.
With the dye module, you get two randoms. You could buy 10 of them (2,000 CC) and get neither black/black or white/white. Or you can pay upfront for one with no worries.
One thing to consider though, is most people have a "favorite" chest armor graphic that they use all the time. They just change the mods to it. This lessens the chance that you replace the chest soon.