I need a formula for a budget I am drafting with estimated and actual costs.
Column B is estimated costs, Column C is actual costs. I can SUM the numbers
in Column B for the estimated total cost but for the actual total cost I need
to SUM the numbers in Column B unless there is a number in Column C that is
different, in which case I would like to use the value in C for that item
instead of B.

I am Excel illiterate so thanks for any help!