The prices filed by manufacturers and others authorized to sell alcoholic liquors to licensed distributors, pursuant to subsection (1) of Kan. Stat. Ann. § 41-1101, shall be the current prices, F.O.B. point of shipment, and said price as filed by each manufacturer or vendor shall be as low as the lowest price for which the item is sold anywhere in any state in the continental United States by such manufacturer or vendor: Provided, That in determining the lowest price for which an item of alcoholic liquor is sold in any such state there shall be taken into consideration all advertising, depletion and promotional allowances and rebates of every kind whatsoever made to purchasers in such state by the vendor.