In establishing the cost of merchandise to the retailer or wholesaler, the invoice cost of such merchandise purchased at a forced, bankrupt, closeout sale, or other sale outside of the ordinary channels of trade, may not be used as a basis for justifying a price lower than one based upon the replacement cost of the merchandise to the retailer or wholesaler, within thirty (30) days prior to the date of sale, in the quantity last purchased through the ordinary channels of trade.