That is certainly possible in Filemaker, but there are many different possible approaches and you do not describe the current design of your database. Without that information, a suggestion on how to do this may assume a design very different from what you have.
A typical system for estimates, invoices and/or purchase orders have the following relationships and tables:
The name of the second table will depend on what one record in the table represents, but the basic relationships remain the same. LineItems is were you would list the individual items and services for that specific estimate, quote, invoice or purchase order. The last table lists your standard products and services that you supply to your customer along with the unit costs for each.
Does this look like what you have in your database?