A single father, a middle-aged woman and a young family are some of the Nevada County residents who are taking advantage of still-low housing prices to get into their own homes.Median prices continue to plunge: The median price of all houses and condominiums that closed escrow in March for all of Nevada County was nearly $239,000, down 25 percent from a year before, according to DataQuick Information Systems, a tracking firm in San Diego.But "sales are up," said Diane Helms of Sierra Gold/ERA Cornerstone Realty.And low prices offer "great opportunity," she added. "Interest rates still are good. It's not easy. …