All consumer commodities designated by the commissioner in accordance with subdivision (a) of section 20-710 hereof exposed for sale or offered for sale shall be plainly marked by a stamp, tag, label or sign at the point of display with the appropriate price per measure; provided however, that the provisions of this section shall not apply to any food store having had annual gross sales in the previous tax year of less than two hundred fifty thousand dollars, ($250,000) unless it is a part of a network of subsidiaries, affiliates, or other member stores, under direct or indirect common control, which, as a group, had annual gross sales in the previous tax year of two hundred fifty thousand dollars ($250,000) or more.