Any local government may, by ordinance or resolution, authorize joint purchases of materials, supplies and equipment with any private school, parochial school, private college or university or nonprofit human services agency within the local government. The ordinance or resolution shall require that the school, college or agency shall be bound by the terms and conditions of purchasing agreements which the local government prescribes and that the school, college or agency shall be responsible for payment directly to the vendor under each purchase contract. Schools, colleges and agencies shall be exempt from any existing statutory requirements governing competitive bidding and execution of contracts with respect to purchases under this section.