cash value

in relation to the supply of goods supplied under an instalment credit agreement, means—

(a)

where the seller or lessor is a banker or financier, an amount equal to or exceeding the sum of the cost to the banker or financier of the goods, including any cost of erection, construction, assembly or installation of the goods borne by the banker or financier and the tax leviable under section 7(1)(a) in respect of such supply by the banker or financier; or

(b)

where the seller or lessor is a dealer, an amount equal to or exceeding the price (including tax) at which the goods are normally sold by him for cash or may normally be acquired from him for cash (including tax) and any charge (including tax) made by the seller or lessor in respect of the erection, construction, assembly or installation of the goods if such charge is financed by the seller or lessor under the instalment credit agreement;