Send Weekly Collections to Clients with Open Invoices

I’ve been trying to create a workflow that takes my invoice aging report, group them by customer and then send an email to clients with all their open invoices. I’ve tried using a CSV file to then batch everything but I’ve been using my max operations merely testing the workflow. I’m doing something wrong, as there’s no way I should be using thousands of operation credits to send collection emails once per week. Any ideas on a good workflow?