Hey David,
On our forum we will always give our users a good push in the right direction, but we will not be able to lay out step by step instructions. We do offer Consulting Time, where you can work with your Business Consultant 1 on 1 to get some work done.
To get you started..
You will need to capture the customer on the Invoice/Estimate. Then retrieve the Price Level from the customer table and use that in your calculations.
Hope this helps.