San Francisco’s iconic cable cars are turning into a budget-busting headache — as city officials are already begging voters to rescue the struggling transit system. The historic cars cost an eye-popping $871 per hour to run — nearly three times the systemwide average, according to a new report from urban police group SPUR . That revelation comes at a precarious moment for the San Francisco Municipal Transportation Agency, which faces a ballooning deficit that could reach $434 million by 2030.