Ok thanks, it's a pity there is no tool available.
The problem of check price of every subcomponent is that each one has their own price history, so to know the price history of the legendary sigil one should add each subcomponent history together, which I don't think it is feasible without making it run automatically with some script.
Checking a historic thread is a solution to have a spot price in that historical moment, but it is not possible to find this for every crafting item and again it does not give full price history. I'm surprised no one ever implemented this, maybe it is too difficult, I have no idea