Tip : Data Validation is a very weak control mechanism. When you copy and paste a value in a cell, all data validations are by passed.
For the sake of a solution, lets assume that the currency cells are A1 and B1 on sheet1.
Goto the code of sheet1 in VBE and write a macro, something like this
Dim lOldVal As Long 'Sheet Module level variable
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$A$1" Or Target.Address = "$B$1" Then
If Not IsNumeric(Target.Value) Then
MsgBox "Only numeric values allowed.", vbInformation, "Foo"
Application.EnableEvents = False
Target.Value = lOldVal
Application.EnableEvents = True
End If
End If
End Sub
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Address = "$A$1" Or Target.Address = "$B$1" Then
lOldVal = Target.Value
End If
End Sub
change $A$1 and $B$1 with your actual cell address.