Here are some great resources to help you fill out that fun recipe costing sheet and figure out just how much a serving of your recipe will cost.
This is the paper version - that you fill out with a pencil . .  . old school
Here is a nice and easy online version that does the math for you . . . BUT you will still need to do any needed conversions ahead of time - like how many cups of sugar in that 25 lb bag of sugar???  
Save yourself a trip to the store - you may use current prices from Safeway as your guide.  AND - check below
There is an excellent app for your phone called Kitchen Calculator PRO that I LOVE and probably use on a daily basis.  But if you don't want another app on your phone - use this website to figure out how many Tablespoons of flour are in a 10 lb bag. . . . cause your recipe probably doesn't call for pounds, right???
To get you started - here are a few common ingredients and our cost:
White Granulated Sugar .20 a cup
Brown Sugar                       $1 a cup
Flour                                      .09 a cup                                    
Eggs                                        .11 each
Butter                                    $1.35 a cup
Margarine                             .65 a cup
Milk                                        .25 a cup
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