You got it. For this size of a database I really don't see the problem with storing unit price data with each order detail. This way you don't have to maintain price data seperately. But I have to be concerned with how the form of everything is going to be analyzed. I have all of my relationships laid out. I've not done my data dictionary yet. I was wanting to make sure I have enough of the app working before I lock myself into a design.

To answer your questions-

1. Is this a multicurrency system?
No. American dollars only. The end application will be used by a local pool construction subcontractor.

2. Will it supply different customers at different prices?
No. Right now on the invoice form there is a field to input a discount for that particular item. I currently do not believe that my customer needs this functionality. So I'll probably remove it from the form.

3. Are their variable sales tax rates?
No. Everything that is billed is for labor. His customers by the parts and supplies. He picks them up using a PO number, and then just bills back for labor.