Two or more municipalities may jointly acquire real property by condemnation, purchase or gift, for airport purposes, and may jointly establish, construct, equip, maintain and operate an airport thereon for the joint benefit of such municipalities. The governing body of each participating municipality shall adopt a resolution authorizing and directing the president, mayor or other member of such governing body to enter into a contract with the other named participating municipality or municipalities for the acquisition, establishment, construction, improvement, equipment, maintenance, operation, regulation, government or financing of the joint airport. The form and terms of the contract authorized to be executed shall be set out in full in such resolution. Whenever there shall be, or exist, any officer, board, department, agency or instrumentality of the United States or of the State of Alabama authorized to negotiate such a contract upon behalf of its government, creator or principal, one or more municipalities may, through such authorized officer, board, department, agency or instrumentality, enter into a contract with the United States or the State of Alabama, or both, for the acquisition, establishment, construction, improvement, equipment, maintenance, operation, regulation, government or financing of a joint airport for the joint benefit of the participating governments, such contract, or contracts, to be authorized by such municipality or municipalities in the same manner as that prescribed in this section for authorization of contracts between municipalities. Each participating municipality may pay its proportion of the cost of any joint enterprise authorized by this section out of any funds which it is authorized to expend for the acquisition, establishment, construction, improvement, equipment, maintenance or operation of an airport for its own separate benefit.