After obtaining the review and advice of the governor’s advisory committee on vendor rates, the secretary shall establish rates of payment for services which are to be purchased: PROVIDED, That the secretary shall afford all interested persons reasonable opportunity to submit data, views, or arguments, and shall consider fully all submissions respecting the proposed rates. Prior to the establishment of such rates, the secretary shall give at least twenty days notice of such intended action by mail to such persons or agencies as have made timely request of the secretary for advance notice of establishment of such vendor rates. Such rates shall not exceed the amounts reasonable and necessary to assure quality services and shall not exceed the costs reasonably assignable to such services pursuant to cost finding and monitoring procedures to be established by the secretary. Information to support such rates of payment shall be maintained in a form accessible to the public.