Grouping Same Part Numbers And Adding Their Prices

I have the following Macro which groups same part numbers in an excel sheet and also creating a blank row after each (or set of same) part numbers. Their prices are in the adjacent cells. I want to add the price cells and the total to appear in the blank cell below the prices.
I have one part number in Cell say A1, Its price in Cell B1
i have another same part number in A2, its price in Cell B2
(The macro has grouped them together)
Now I want to add cell B1 & B2 and the result in B3 (Row 3 is blank, created by a macro after each group of similar part numbers)

This process is to be repeted in the entire worksheet.

Sub InsertRow_At_Change()
'part number
Dim LastRow As Long
Dim X As Long
LastRow = Cells(Rows.Count, 1).End(xlUp).Row
Application.ScreenUpdating = False

For X = LastRow To 3 Step -1
If Cells(X, 1).Value Cells(X - 1, 1).Value Then
If Cells(X, 1).Value "" Then
If Cells(X - 1, 1).Value "" Then
Cells(X, 1).EntireRow.Insert Shift:=xlDown
End If
End If
End If
Next X
Application.ScreenUpdating = True
End Sub