(a) This section does not apply to a "health and human services agency," as that term is defined by Section 521.0001, Government Code.
(b) The executive commissioner may allow a state agency, local agency, or local mental health authority that expends public money to purchase goods or services in connection with providing or coordinating the provision of mental health services to purchase goods or services with the public money by participating in:
(1) a contract the executive commissioner has made to purchase goods or services; or
(2) a group purchasing program established or designated by the executive commissioner that offers discounts to providers of mental health services.