Assistance: Conditional formatting comparison between two FILES.

[omni13]

Scenario:
I have a new task that I may need some help wrapping my head around. I decided to ask here while I also attempted to come up with a solution. I have two different excel files. A budget, and an expense file. Each has many processes to determine numbers. I think the best method would be to duplicate them and simply add the Expense processes to one of them.

Budget file/sheet has estimated costs.
Expenses are actual costs.

My question:


How would I go about setting up conditional formatting on 2 years+ worth of months to compare budget expense values between the two files. Also is this possible? To read from a closed file or pull information from it to compare? I would want differences to be red for greater than value, yellow equal, and green as less than. As well I don't formating to be broken if new columns are added. Would I have to manually add range names to the cells?

Any assistance would be greatly appreciated!

Edit: I added one of the sheets I look to duplicate. or insert into another file where expenses are housed. I threw in some arbitrary numbers to sample.