The weekly broadcasts of the Metropolitan Opera, under threat ever since ChevronTexaco quit as principal sponsor in 2003, have found a new benefactor in an unlikely place. Toll Brothers, a home building company based in suburban Philadelphia, has agreed to sponsor the broadcasts for the next four seasons. The broadcasts cost $6 million per year, and the Met says that Toll Brothers has agreed to pay a “major” portion of that cost. The company, which specializes in high-end luxury housing (its average home sells for $600,000 or more) is hoping that the association with the Met will add an element of class to its image in the eyes of prospective clients.