Pat,
Can you explain this in more Detail? Do I bring up the report and go to the Source for the Units, Rate, and Hours fields and enter this formula in each of those Fields?
Select fld1, fld2, fld3, IIf(NZ([Units],0) = 0, [Rate]*[Hours], [Rate]*[Hours]/([Units]) As TotCost, fld4, ....
From...