In this Act, unless the context otherwise requires,-

(35). "purchase price" means the amount of valuable consideration paid or payable by a person for the purchase of any goods, less any sum allowed as cash discount, commission or commercial rebates granted at the time of delivery, or before delivery, of such goods but including cost of freight or delivery or distribution or installation or insurance, or any sum charged for anything done by the seller in respect of the goods at the time of delivery of such goods or before delivery thereof, other than interest if separately charged;