The prices of these materials relative to one another in bulk terms, vary greatly with time as the constituent metals of the alloys change in price. Nickel has varied between $3 and $25/pound in a period of as little as a decade. And yes, quantity and product form (as well as forged/wrought or cast) matters a great deal.
You can find some old charts of the alloy relative prices in piping systems, which were developed by Fluor in the 1970s and listed as a figure in Perry's Chem Eng Handbook, but they're obviously made rubbish by fact of their age- and they don't include duplex.
Ferallium 255 is a cast only grade. Hastelloy isn't an alloy, it's a trade name. There are many Hastelloys.
Actually ATI is making 255 plate.
And the same comment about being a general name goes for Monel, there are 4 or 5 of them commonly used.
The reason that product form matters is that some alloys are really only made as plate, or bar. If you are building a plant and want to use all super duplex, by the time you get plate, bar, tube, pipe, forgings, and castings you may have four different alloys. And some of them will be twice the cost of others because of the combination of grades and product.
Thanks to you all, I appreciate all input.
I am totally aware of the parameters that can affect the comparison
in time however I am just looking to receive comments from different
parts to prepare a guide for myself. However no one wanted to give figures.