Using vlookup without overwriting values that isnt in the lookup sheet

NorthernKarsten 

You cannot use a formula in column B for this - it would lead to circular references.

You can simply copy/paste the new prices, or if you prefer, run a macro:

Sub UpdatePrices()
    Dim r As Long
    Dim m As Long
    With Worksheets("Item price sheet")
        m = .Range("A" & .Rows.Count).End(xlUp).Row
        For r = 2 To m
            If .Range("C" & r).Value = "A" Then
                .Range("B" & r).Value = Application.VLookup(.Range("A" & r).Value, _
                    Worksheets("Factory A New Prices").Range("A:B"), 2, False)
            End If
        Next r
    End With
End Sub