Comparisons between rates

I have a table that looks something like this

etc

I would like to make a comparison between two different supplier contracts that give rates based on the weight. Then once I make the difference between two sets of rates, I would like to multiply this by a customers real volume per weightbracket and iso to determine which supplier contract is more expensive. I am having trouble figuring out how to do this, since filtering in any way filters the other values as well. Any ideas?