Calculate the Fair Value of raw materials that are related to Copper

Job ID: 33080540

Budget: €8 – €30 EUR

I work in a manufacturing company and we buy raw materials that their price is directly correlated to Copper.
There is a way that we examine if the price they offer us is fair taking into account the Copper Price and the price per piece percentage change from our last 3 offers.
I want to know if there is another way to perform this calculation in an excel spreadsheet.
Related categories: Data Processing Excel Statistics Mathematics