We are a consultancy firm and are having the same issue.  Unfortunately, the answer is always "export to Excel".  It would be nice if QB was one large database or had the ability to link it's separate databases for purposes of reporting.  All the manual work defeats the purpose of the accounting software.  Since the estimate was converted to an invoice by QB, it should have a link between the two sets of data, which should then translate into pulling a report using any of the information found in both the estimate and the invoice.

Good luck!