It seems the Tortured Gift of Living Steel chest that drops boss summon materials is a bit cheaper than advertised! Grigoire aka the Galvanic Saint is summoned by gathering 5 Living Steel materials that only drop from the Helltide chest.
The chest is marked as requiring 300 Aberrant Cinders, but you actually only need 280 to pop that thing open. We can see as much below:
It’s not a huge difference, but it definitely helps! So get on in there and grab that steel so you can face the Saint and then get those ever-important Duriel mats from him (and whatever uniques he might drop as well).