Can you elaborate little further on your cost per item based shipping calculation? Do you want to specify unique shipping rate for each product or group of products?
From what i understood I think, Shipping Rates by ZipCode app is 100% match for your requirement. This app supports shipping rates based on ZipCodes with lot of Conditions like Products selection, Price, Weight, Qty and many more.
Its multi-feature app and you can setup various conditional logic as per your requirement:
You should give it try and contact support for professional setup service at zero cost.
See if this helps.