ExcelBanter - Pivot Table Comparison

Hi all,
I am hoping t get some help on this.

I have two worksheets of monthly data (last month and current month) that
gets updated at the end of each fiscal month. I pull the data into two pivot
tables on the third sheet and am trying to put a formula together to compare
the pivot table data. Here is an example of the data in each pivot table:

In the old file:

Charge Number 1234 was used for resource 12 ($300), resource 34 ($1,000) and
resource 56 ($600).

In the new file:

Charge number 1234 was used for resource 12 ($800), resource 34 ($1,400),
and resource 56 ($250).

What I want to do is pull data into pivot table, find differences between
the months and show the difference (delta) in a different column. The catch
is that I want it set up for monthly use so I don't have to re-do formulas
and workbooks every month. Also, not every esource is used eery month, so it
has to be a little dynamic as well.

Any suggestions?