Hello,
I think I can supply you just the thing you need. Actually I plan to use VBA codes and Excel forms elements (like dropdown lists, text boxes, buttons etc) to achieve your goal.
From your description, I understand that you'll enter the some details manually first (after the products are purchased, details like the name of the vendor, product descriptions etc), select and enter the category name (from perhaps a dropdown combo box I'll make for you), and in this way develop the database.
Automation shall be needed in finding the cheapest price per product (according to vendors), then perhaps select that product / products, and finally create an invoice from there.
All these can be achieved with VBA Codes and excel forms. If you could supply me a format of the invoice, that would be best.
So please feel free to message me if you need more clarification.
Thank you and Best Regards
Raad