Dropshipping items from mutiple companies

Here is our problem, we have multiple manufactures of our products each with a different shipping calculation. We need to calculate the shipping costs of shipping for each item by manufacture and then if it is international or not. I expect to have to modify a shipping module but I'm not sure which one would be best. Also has anyone already tackled this and give me some clues.
:frusty:

Is the shipping based on Weight, Item Count or Price, by each manufacturer?

What is the difference then for the International vs National?

Item count of each manufacturer.

customer buys 6 items from Manufacturer A & 1 item from B.
shipping = (A's shipping * 6) + (B's shipping * 1)

Some of the manufacturers have different rates when shipping outside of the USA & Canada and some don't.

international customer buys 6 items from Manufacturer A & 1 item from B. B has both national & international shipping rates
shipping = (A's shipping * 6) + (B's international shipping * 1)

How many Manufacturers do you have?

For a given Manufacturer, are the rates for National and International the same for all of their Products?

Right now, 120. Currently the international shipping rates stay constant for a given manufacture.
The actual problem is with the suppliers who do the drop shipping, we have less that 10 right now but it could grow. I used manufactures because I couldn't see anyway to group by suppliers.