For purposes of this article, the term:
(1) "Affordable housing" means housing that could be purchased with a cash down payment of at least ten percent and the proceeds of a mortgage loan, the monthly principal and interest payments on which do not exceed thirty percent of the gross monthly income of a household earning one hundred percent of the current median family income, as computed by the United States Department of Housing and Urban Development, for the county in which the district is located. For the purposes of this definition, the monthly principal and interest payments referred to in the preceding sentence are computed using a standard amortization calculation incorporating the prevailing annual rate of interest on mortgage loans offered by financial institutions in the vicinity of the district, as determined by the Development Office at the time of its review of a municipality's application in accordance with section seven of this article, and a thirty year amortization period.