The authority may enter into contracts of sale with any participating party covering any project financed by the authority. The purchase price pursuant to such contract of sale shall be sufficient to provide funds for all the purposes provided in Section 44551 and may be paid in installments, together with interest on the unpaid balance, or otherwise, as may be mutually agreed and set forth in such contract of sale. All payments received by the authority under any installment sales or conditional sales contract shall be applied by the authority substantially in the same manner as hereinabove provided in Section 44551 in the case of lease payments or rental charges received by the authority.