PITTSFIELD — From a modest, $79,900 two-bedroom home in North Adams to a 4,400-square-foot jaw-dropper priced at $3.2 million in Monterey, the homes for sale in Berkshire County opened their doors yesterday in a mass showing of available real estate.For the first time, the Berkshire County Board of Realtors organized area real estate agents to stage an open house extravaganza. From North County to South County, roughly 340 homes had open houses in the morning and afternoon hours.