Excel: If we have 5 different suppliers of same products having prices as per their policies, we have to extract that which supplier is cheapest in which product or which product should we purchase from which supplier. Which formula we can use?

If the column A - supplier, column B - product, column C - the price, in the D column you want to insert the formula ={IF(MIN(IF($B$2:$B$10=B2;$C$2:$C$10))=C2;1;0)}. A value of 1 - the lowest price. A value of 0 - non-minimal price.

you need to use 

min(): to find the minimum for selected supplier

index(), match(): to allocate target cell or cells

you should use both of the below formulas: V lookup/H lookup - to make a search field to determine the companies that you are looking for, then you have to use : =MIN for the price field to determine the cheapest price also you can not use any formulas, you can only use the Conditional formatting to determine prices based on different criteria.