On the eve of a hearing on plans to charge drivers to enter lower Manhattan, boosters of the plan said Monday the money would buy Bronx commuters more public transit.The Campaign for New York's Future, a coalition of more than 70 civic and business groups promoting Mayor Bloomberg's congestion pricing proposal, gathered on the steps of the Bronx County Building to tout the transit improvements promised to the Bronx if the controversial vehicle charge is approved.The plan would charge $8 for cars and $21 for trucks driven south of 86th St. between 6 a.m. and 6 p.m. weekdays.Bronx critics of the plan worry it will cause worse congestion in the asthma-choked South Bronx, with commuters driving there to park before taking the train into Manhattan.But boosters argued yesterday that the mass transit improvements to be funded by congestion pricing would actually reduce local daytime traffic."I believe congestion pricing is one of the keys to reducing automobile traffic and carbon emissions throughout the city," said State Sen. Jos