A general approach could be to have a summary field to calculate the Minimum Record ID# of the Entry (or maybe you call them Cost Sheets) for the vendor which does not yet have a Purchase Order created.
Then you would have an Automation fire to Create a Purchase Order for that Vendor. (I'm not quite sure yet how you plan to attach the entries to the Purchase Order....)
so that will have solved for the first Purchase Order.
The run the Automation again and it should find the next Entry which needs a Purchase order for the next Vendor.
So provided that in fact you do not have an infinite number of Unique Vendors but a reasonable maximum of say 10 per Cost Sheet, then just run the steps 10 times in the same automation. You get 50 steps per Automation. You may need to create a dummy table to summarize up the highest Record ID# of the Purchase orders so the Automation or saved table to table import that the Automation runs, knows where to attach the Entries.
