(g) notwithstanding anything contained in clauses (c) and (a), the cost of construction and the market price of the land comprised in the premises purchased from or allotted by the Government or a local authority shall be the aggregate amount payable to such Government or the local authority for the premises: Provided that the Rent Authority may, for the purpose of arriving at, the cost of" construction and the market price of the land comprised in the premises. allow addition, subject to a maximum of thirty per cent. of amount payable to the Government or the local authority, to the amount so payable for any expenditure incurred by the landlord or by the first or any subsequent purchaser or allottee for any improvement, addition or structural alternation in the premises.