Sigil of Fortification

High alchemy turns Sigil of Fortification into 6,000 gp. Buying one at 50,000 gp (its guide price, as it has not traded today) and casting with a nature rune at 137 gp costs 50,137 gp. That is a loss of 44,137 gp per cast at its guide price, so it is not worth alching for profit right now.