Overwriting Formula With A Value But Still Keep Formula If Value Is Deleted

I would like to use the code below such that column "A" contains unit list pricing, Column "B" calculates the discount from the net pricing in Column "C." For example, A1 = 100, B1 = 1- (C1/A1), and C1 by default is equal to A1 but if the user enters in a net rate, say 85 in C1, it retains the 85 in C1 but if then later deleted, the C1 automatically reverts back to =A1. The code below works great for C1 but for the life of me, I cannot figure out how to modify the code and have it work correctly for a range of cells in Column "C" or all of Column "C."

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
With Target
If .Address(False, False) = "C1" Then
If IsEmpty(.Value) Then
Application.EnableEvents = False
.Formula = "=A1"
Application.EnableEvents = True
End If
End If
End With
End Sub