bears rents not greater than the lesser of (i) the existing fair market rent for comparable units in the area as established by the Secretary under
section 1437f of this title, or (ii) a rent that does not exceed 30 percent of the adjusted income of a family whose income equals 65 percent of the median income for the area, as determined by the Secretary, with adjustment for number of bedrooms in the unit, except that the Secretary may establish income ceilings higher or lower than 65 percent of the median for the area on the basis of the Secretary’s findings that such variations are necessary because of prevailing levels of construction costs or fair market rents, or unusually high or low family incomes;