Any purchase or lease of goods, professional or nonprofessional services, or for the purchase of insurance, construction, or construction management, when the estimated cost thereof shall not exceed $500, shall be deemed a small purchase and shall not be subject to the rules governing open market transactions. However, the Georgetown University Director of Administrative Services shall, wherever possible, attempt to place small purchases with vendors having an existing contract with the Georgetown University or who have registered on the Georgetown University Procurement Opportunities List.