If you repeatedly have one time vendor purchases, I would encourage you to work with Purchasing to set up a P-Card policy. This utilizes a credit card (Purchasing Credit Card) and establishes a dollar limit, process/procedure, and audit trail.
Quick online / Google search will provide corporate level examples outlining multiple programs that will work with several ERP systems. End users place requisitions and Purchasing utilizes the P-Card for the transaction, providing a less cumbersome process. We call this streamlining P to P (Procure to Pay), eliminating several steps outlined in the link previously provided.
Let me know if you would like any additional information.
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