Each state agency, excluding public, private, or independent institutions of higher education, must purchase any commodity items that are listed under the commodity codes under the department's responsibility in accordance with a contract developed by the department, unless the state agency first:(1) obtains an exemption from this requirement as described by Subchapter C of this chapter;(2) obtains express prior approval from the Legislative Budget Board for the expenditure necessary for the purchase; or(3) obtains a certification from the department, as described by Subchapter D of this chapter, that the commodity item is not available for purchase under an existing contract developed by the department unless the value of that contract exceeds $10 million dollars.