In this Act, unless the context otherwise requires,-

(31) "Sale-price" means the amount payable to a dealer as valuable consideration for the sale, other than that referred to in section 15, of any goods, less any sum allowed as cash discount according to ordinary trade practice, or any sum charged as cess leviable or a sum equal to the sum charged from a registered dealer by another registered dealer as cess leviable under the West Bengal Transport Infrastructure Development fund Act, 2002 but including any sum charged for anything done by the dealer in respect of the goods at the time of, or before, delivery thereof, other than the cost of freight or delivery or the cost of installation or interest when such cost or interest is separately charged ;