Ribbon, along with rent, was cut at a Williamsburg ceremony Friday that marked the opening of an affordable housing complex.Renters will pay $500 to $600 a month for one, two and three bedroom units with living rooms and kitchens. Developers hope the $2 million South Second Street, built to house 25 families, will attract working class tenants. Hundreds are expected to apply for admission to the unit, named after Monsignor Brian Karvelis, a priest who was active in the community.Applications can be filed with developers now through December 31. Another unit for low income seniors is planned in the same vicinity.