Automated purchase invoice entry

A building contractor which has grown strongly in the last few years, has seen the number of purchase invoices rise to more than 2000 per month.  As the number continues to grow, I need to implement an automated solution to read the invoices, match them to orders and then put them into the system, where they can then be electronically approved.  The accounts system is Sage 50, slightly complicated by the use of Sage Construct to manage each project/site.  I would welcome advice from members who may have already invented this particular wheel!