Students can't afford to fill Pittsburgh's budget gap, many of them told the City Council yesterday at a hearing that started with a request for a college president's salary, and turned into something of a contest for the title of least-well-off scholar. The city's annual budget hearing focused on the 1 percent tuition tax that Mayor Luke Ravenstahl has proposed in an effort to find $15 million a year to bail out the city pension fund. The proposed $453.8 million budget won't rely on the tax, and a tentative vote on the levy would be just the beginning of a lengthy fight that could move to the courts and Harrisburg.