Sumif function

[SRobson]

I need to sum data in cell(s) in the same column whose reference is derived
from:

Row: Heading of the column the formula is in
Column: Data that is in column of the cell the formula is in.

The columns where the headings can be found will change, so needs to be
dynamic, otherwise this would be straigh forward.

Basic example of vast data array:

Column A ? ?
Department Tax Payroll
Tax -10000 (Sum of payroll figures/count of Tax)
Payroll -50000 (Sum of Tax figures/ Count of Payroll)
Payroll -30000 (Sum of Tax figures/ Count of Payroll)

Kind regards.