It shall be the duty of the state board to fix prices at which the various instructional resources on the state multiple list shall be sold to patrons, the excess of which above contract price shall represent the profit to the retailer; but in no case shall such profit exceed twenty percent of the contract price. The state board shall notify each county superintendent of the instructional resources on the state multiple list and the prices at which they are to be sold, and any person selling such resources at a higher price than that fixed by the state board shall be guilty of a misdemeanor, and, upon conviction thereof, shall be fined not less than $10 nor more than $50.