I've got a very simple spreadsheet that I call my "orthodontics sheet". With this, I plug in my price and the weight I buy my ingredients in (ie walnut 1/2's and pieces, $32.69 for a 5 lb re-pack) and it spits out a price per kg.
EVERTYTHING in my kitchen is costed out in $/kg, including oil, booze, milk, cream, spices, etc. All of my recipies are in metric weight as well. It doesn't matter what the packaging size is or if it is in imperial or metric, all that matters is your price per kg. Once you do this you will see the actual prices you pay much easier and helps you deal with sales reps.
Not only does this ($/kg) make costing a lot simpler, it makes the recipies much easier and faster to scale out, fewer mistakes (no fractions of ounces, ounces by weight or volume, level cups, scant teaspoons, etc) but inventory is a whole lot easier, you just plop your stuff on the scale and X $/kg and you're done.
It is a lot of work to change all of your recipies from imperial volume to metric weight, but once you do, you will never go back, and wonder why you never did it earlier.
Hope this helps