I've been looking for exactly this function for days now. Can't seem to find it. The closest I've found is the App Supply Order by happyj. But it can't read all of my inventory items and there seems to be no 'key' to what it can and can't read, so I can't modify anything. Very frustrating! The App Stitch is awesome, but it's a full invoice & inventory list. But lacks any kind of expenses/marketing/template funciton.
A purchase order (PO) is a commercial document and first official offer issued by a buyer to a seller, indicating types, quantities, and agreed prices for products or services. It is used to control the purchasing of products and services from external suppliers.
The Cheesy Animation :-
We've just release a new Purchase Orders app here https://apps.shopify.com/purchase-orders-1
You can also try it out for 30 days.
Hope this helps