A good idea but I'd bet actual money that pirates would simply up their demands in response, the few pirates I'd had the pleasure of meeting have usually had incredibly detailed information on every single tradable commodity knowing full well how much of a profit awaits at the end of the route. The worst of the worst will still make high demands just to get the kill or refuse to pay regardless.
I do like splitting commodities into pricing strata so long as each company could access a couple of basic and luxury items apiece.
