The item I ordered costs $4950 and the supplier charged me $51 in shipping. Is a requisition required?

Yes, a requisition is required because the total amount of the order, including shipping, exceeds the $5,000 purchasing threshold.

Read more:

• Purchasing Manual: Introduction to Procurement Processes, Chapter 2: Purchasing Processes > Purchasing Thresholds
• Purchasing Manual: Introduction to Procurement Processes, Chapter 6: Best Practices