Assistance: Conditional formatting comparison between two FILES.

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.

Apologies, I had to first comb through and remove any information deemed sensitive as I am using copies for learning purposes. Uploaded in original post.

I will reiterate the situation:

Sheet1: Column A: lists contractors. Rows Contain Months of the year.

Sheet 2: Same items, but many more values in Contractor List.

Months between the two sheets are common.
**Some** Contractor names will be common.

The values that will need conditional formatting will be those values in the middle, intersecting months and contractor name.

How would I get Contractor Names List from Sheet1 to be compared to those in Sheet2, then the values in their respective rows need to be compared with conditional formatting? So basically as it is set up in the attached document. The example has the yellow numbers highlighted. If say I had another sheet similar to this one in another file, is it possible to achieve it?