The price of stainless steel is made of of two components, the base price and the Alloy Adjustment Factor (AAF).
The base price is based on the manufacturers cost for producing the material to a certain specification.
The AAF charge is for various alloys used (e.g. nickel, molybdenum) to produce the specific grade.
View the November 2017 update here
Nickel also undergoes dramatic price changes - view the last 3 months of Nickel price changes here