Help with % splits

Ok.. these things always seem hard to explain over a forum, but I'll give it a shot:

I have a number of factories (lets use 4 in this example, but actuals are over 3,000). Each factory produces a number of items. Not all factories produce all items. In this example, lets use a total number of 4 items, but in actuality the number is closer to 75.

So, here is a list of the factories, and the amount of each item they produce:
Factory 1 Item 1 $540 Factory 1 Item 2$312
Factory 1 Item 3 $95 Factory 1 Item 4$500
Total Factory 1 $1447 Factory 2 Item 1$120
Factory 2 Item 2 $75 Factory 2 Item 3$89
Total Factory 2 $284 Factory 3 Item 2$410
Factory 3 Item 3 $412 Total Factory 3$822

Factory 4 Item 1 $1000 Factory 4 Item 4$942
Total Factory 4 $1942 Here are the totals for each Item: Item 1$1660
Item 2 $797 Item 3$596
Item 4 $2389 Finally, my problem: I want to move the total amount that each factory produces (the overall amount won't change), so that each Item's total will not change. So for example, I want the output of Factory 4 to go from$1942 to $1342 (-$600), Factory 1 to go from $1447 to$1247 (-$200), Factory 2 to go from$284 to $984 (+$700) and Factory 3 to go from $822 to$922 (+$100). When those changes are done, the total for Item 1 will still be$1660, Item 2 still \$797 and so on...

The 2nd piece to my problem:
I've laid this out in Excel and there are basically an infinite number of solutions. The solution I am looking for is where the total amount of change from each Factory will be either spread proportionally across all Items produced at that factory, or spread proportionally across how all Items are produced nationally.

I know that was hard to get out, but hopefully someone out there understands what I'm getting at and can lend a hand.