Do you have sample data you can provide or a workbook to show how the data is setup? In the past, I've just setup a simple calculated field that is written out to be SUM(Cost Difference between Planned and Actual)/SUM(Planned Cost) but I'd have to see how your data is constructed to determine what the best route would be for your data and why the calculations you've created haven't worked.
If Column 2 is already an aggregation, then you probably just need to eliminate SUM from that part of your calculation. Something like:
SUM([Planned Cost])-([Difference Between Plan and Actual])
I set something similar up in the attached.