Change a cell populated by a dropdown when the value of the source range changes

The only way to do this I know of is through VBA. When you use the drop downs to select a value on the LABOR sheet, the selection is immediately replaced with a formula that gives the same result. This way if you go back and change the Assumptions, the new values flow back to your previous selections on the LABOR sheet.

This has been added to the LABOR sheet code module:

Option Explicit

Private Sub Worksheet_Change(ByVal Target As Range)
'Author:    Jerry Beaucaire,  8/12/2011
'Summary:   Make choices from DV drop downs into formulas, so any changes
'           in the source lists will flow out to the already filled in cells
Dim strValidationList As String
Dim strVal As String
Dim lngNum As Long

If Target.Cells.Count > 1 Then Exit Sub
If Target.Value = "" Then Exit Sub

On Error GoTo Nevermind
strValidationList = Mid(Target.Validation.Formula1, 2)
strVal = Target.Value
lngNum = Evaluate("MATCH(" & strVal & ", " & strValidationList & ", 0)")

If strVal <> "" And lngNum > 0 Then
    Application.EnableEvents = False
    Target.Formula = "=INDEX(" & strValidationList & ", " & lngNum & ")"
End If

Nevermind:
    Application.EnableEvents = True
    
End Sub

Before that would work, however, I had to fix the decimal errors hidden in your ASSUMPTIONS. When you multiply decimal values the results are almost always LONG decimal values. $ values stop at 2 decimal values so your number formatting was hiding the errors. You should always apply rounding to decimal values that have been multiplied to insure the DISPLAYED value is the real value in the cell.