The central postal system chief, under the direction of the department of administration, shall cause to be metered all such outgoing mail and shall be responsible for the keeping of records and costs thereof, and shall be able to at least monthly certify to the state controller the amount expended on behalf of each department, agency or institution directly utilizing the central postal system, which amount shall be charged against the funds of such department, agency or institution and continually appropriated to the account of the department of administration for the operation of the central postal system. Those agencies which expend funds for stamps and metered postage directly shall make expenditure reports available to the department of administration at least semiannually. The department of administration shall annually submit in the department budget request an accounting of the total cost of postage to the state, as well as the calculated savings and the methods through which such savings were derived. The central postal system chief is hereby directed to evaluate materials to be mailed and shall cause mail to be properly prepared utilizing the lowest practical and most feasible rate of postage. Provided, however, that each member of the legislature of the state of Idaho shall be issued United States postage for each session attended, in an amount determined by each session of the legislature to be charged to the legislative expense appropriation.