So I've been buying my dust from the inscription trainer for like 10 gold, until i realized the reagents vendor sells it for 31 silver 50 copper. I know its not a huge "WOOOT", but I've probably bought 20-30 dust so far, wasting a ton of gold.
I cant confirm 30 silver to be the price at all the reagent vendors, but Aluril in Wetlands (Greenwarden's Grove) does definitively sell it that cheap.