In all advertisements, offers for sale or sales involving two or more items, at least one of which items is cigarettes, at a combined price, and in all advertisements, offers for sale or sales involving the giving of any concession of any kind whatsoever, whether it be coupons or otherwise, if such rebate or concession offered or given in connection with the sale of cigarettes is not offered or given by the wholesaler or retailer in the same ratio with respect to all other merchandise as to which such rebate or concession may lawfully be given which is sold by such wholesaler or retailer in the ordinary course of his trade or business, the retailer’s or wholesaler’s selling price shall not be below the cost to the retailer or the cost to the wholesaler, respectively, of the cigarettes included in such transactions, and the invoice cost, whether the same be paid by the retailer, the wholesaler or any other person, of all other articles, products, commodities and concessions included in such transactions, to which invoice cost shall be added the cost of doing business in the case of the wholesaler and the retailer, respectively, as such cost is defined in sections 59-1504 and 59-1505.