Check the document in to purchase (Purchase Requisition), check the price with negotiating with the seller, price comparison, document the purchase order/contract.
Check the documentation for the purchase request (Purchase Requisition), check and negotiate a price with the seller, to compare prices, documenting the purchase order / contract.
Check the documentation in the application for purchase (Purchase Requisition), check the price and negotiate with supplier, prepare to compare prices, document order. / promise.