The purchaser shall make an initial payment of at least 10 percent of the selling price of the property, in case of a farm, and 5 percent in the case of a home. The department may waive the initial payment in any case where the value of the property as determined by the department appraisal shall equal the amount to be paid by the department plus at least 10 percent in the case of a farm, and 5 percent in the case of a home. The balance of the purchase price may be amortized over a period fixed by the department, not exceeding 40 years for farms or homes, but not exceeding 15 years for mobilehomes, together with interest thereon at the rate as determined by the department
pursuant to Section 987.17 for such amortization purposes. The purchaser on any installment date may pay any or all installments still remaining unpaid. In any individual case the department may for good cause postpone from time to time, upon terms as the department deems proper, the payment of the whole or any part of any installment of the purchase price or interest thereon. Each installment shall include an amount sufficient to pay the principal and interest on the participation contract to which the interest of the department is subject.