Workflow on sales order price change

SUGGESTED

I am trying to create a workflow to trigger when the net price on a sales order line has been changed. I would like the workflow email to contain both the value before the change and the value after. I am close, but seem to not be able to capture the correct line. If there are 3 lines on the sales order, I get 3 emails when I only want 2 email with the information from the line which the price was changed. 

Here is my workflow and data model. Any suggestions?