The department is authorized to lease by negotiation air rights over existing or proposed limited-access highways for development as commercial enterprises or activities. Prior to entering into any negotiations for the lease of such air rights, the department shall advertise its intent to negotiate the lease of such air rights at least once a week for four consecutive weeks in one or more newspapers of general circulation in the county or counties where the air rights to be leased are situated and in one or more legal organs in Fulton County. Any person, firm, or corporation leasing such air rights shall reimburse the department for all costs, including administrative costs, incurred by the department in connection with the negotiation of said lease. Furthermore, when two or more offers are received by the department for a lease of air rights, the highest responsible offer shall be accepted by the department. The department shall establish a minimum negotiated price, based upon competent appraisal; and the final negotiated amount shall not be less than this appraisal.