How? Think with me:

If, only if, the dust is the equivalent of the "half price in raw materials", and I believe it's simples to assume that this dust is a very raw material, since you can use it in the place of the generic "raw material"...

...then why in Mephisto's name can't you sell the goddamn dust for what it's worth? It's like gems, magical gems and money! Why?

If the awser is "because the OP said so", don't really bother saying it It's a thing so obvious that the OP should review, or else the wole system is flawed from start since things aren't equivalent. It's like buying 500 gp of ruby dust for 450 gp and not being able to use it as material component because you bought for only 450!.