The initial purchase price for all restricted ownership units shall be calculated so that the monthly carrying cost of the unit, including principal and interest (based on a mortgage loan equal to 95% of the purchase price and the FreddieMac 30-Year Fixed Rate-Mortgage rate of interest), property taxes, homeowner and private mortgage insurance and condominium or homeowner association fees do not exceed 30% of the eligible monthly income of the appropriate size household as determined pursuant to N.J.A.C. 5:80-26.7, as may be amended and supplemented; provided, however, that the price shall be subject to the affordability average requirement of N.J.A.C. 5:80-26.4, as may be amended and supplemented.