One way to do this is to use parameters and calculated fields instead of using the filter shelf. Create two integer parameters with the range of the values in COST. Then, create a calculated field that returns null values if the sum(COST) does not meet the criteria within the parameters. I have reattached your workbook showing this. The calculation to refer to is "Cost Range Calculation."
Hope this helps!
Margin v2.twbx.zip 18.0 KB