A person engaged in the business of buying milk, cream or butterfat, either by himself or by another, shall not restrain in any manner open competition in the business, nor discriminate between different sections of the state by purchasing or offering to purchase milk, cream or butterfat at a higher price in one locality than that paid or offered for the same commodity by the person in another locality, but allowance may be made for the difference in the grade or quality of the commodity, and in the cost of transportation from the place of purchase to the place of manufacture, sale or storage.