For 15 years, the Boston Courant has served Back Bay and surrounding communities, bringing  steller, locally-targeted, and professional news in a free (or as they like to put it, "priceless") weekly newspaper and real estate guide.  Like similar free papers, they stay in business via advertising revenue. The staff is cordial, friendly and constantly abuzz in this busy but comfortable office, located on the second floor of 129 Newbury Street, a building they share with no fewer than three art galleries. They do not maintain a Web site.