Используйте общий обработчик событий для CheckBox для вызова метода обновления, подобного этому.
Private Sub CheckBox1_CheckedChanged(sender As System.Object, e As System.EventArgs) Handles CheckBox1.CheckedChanged, CheckBox2.CheckedChanged, CheckBox3.CheckedChanged
UpdatePricing()
End Sub
Private Sub UpdatePricing()
Dim total As Double
Dim pricing1 As Double = 2000.99
Dim pricing2 As Double = 4000.49
Dim pricing3 As Double = 6000.19
If CheckBox1.Checked Then total = total + pricing1
If CheckBox2.Checked Then total = total + pricing2
If CheckBox3.Checked Then total = total + pricing3
Label1.Text = Format(total, "$####0.00")
End Sub