(a) The term “cost” when applicable to the business of retailer shall mean bona fide cost and shall mean: (i) The invoice cost of the product or item of merchandise to the retailer or the replacement cost thereof to the retailer within thirty days prior to the date of sale, offer for sale or advertisement for sale, as the case may be, in the quantity last purchased, whichever is lower, from either of which there shall be deducted all trade discounts, except customary discounts for cash; and (ii) to either of which there shall be added the following items of expense:

(1) Freight charges not otherwise included in the cost of the article, product or item of merchandise, but which freight charges shall not be construed as including cartage to retail outlet if done or paid for by the retailer;

(2) A markup to cover, in part, the cost of doing business, which markup, in the absence of proof of a lesser cost, shall be seven percent of the aggregate of invoice cost or replacement cost (whichever is used), less trade discounts as aforesaid, and plus said freight charges: Provided, That such a markup to cover the cost of doing business as provided for in this subdivision shall be exclusive of any federal and state motor fuel taxes.

(b) The term “cost” when applicable to the business of a wholesaler shall mean bona fide cost and shall mean: (i) The invoice cost of the merchandise to the wholesaler to include applicable taxes, or the replacement cost of the merchandise to the wholesaler within thirty days prior to the date of sale, offer for sale or advertisement for sale, as the case may be, in the quantity last purchased, whichever is lower, from either of which there shall be deducted all trade discounts except customary discounts for cash; and (ii) to either of which there shall be added the following items of expense:

(1) Freight charges not otherwise included in the cost of the article, product or item of merchandise, but which freight charges shall not be construed as including cartage to the retail outlet if done or paid for by the wholesaler;

(2) A markup to cover, in part, the cost of doing business, which markup in the absence of proof of a lesser cost, shall be four percent of the aggregate of invoice cost or replacement cost (whichever is used), less trade discounts as aforesaid, and plus said freight charges: Provided, That such a markup to cover the cost of doing business as provided for in this subdivision shall be exclusive of any federal and state motor fuel taxes.