I noticed that total cost of material to produce an item is typically close to the product value. This however is not the case with Scroll of Ashy Spiketail Summoning and therefore I would suggest for the amount of material required to produce the scroll to be adjusted. Below is a detailed computation of the material cost and product value.
3 Modest Parchment Decor valued at 3 x 12s=36s
Material cost to produce Modest Parchment Decor = 58 Dolomite + 58 Tin Ore = 0.36 x 58 x 2 = 41.76s