Hundreds of Maine residents have signed up for a new state program that pays motorists to junk old cars and buy newer models that pollute less, but regulators have no money to implement the program. The state legislature approved a bill last spring to give vouchers worth $1,000 to $2,000 to drivers who bring in cars from 1987 or earlier and then purchase cars from 1996 or later that meet Maine’s low-emission vehicle standards. Yet it didn’t set aside a pot of money to pay for the program — which could be a real problem, as there may be as many as 200,000 cars built before 1988 on the road now in the state. Regulators also may be in trouble because the program relies on the participation of the 16 auto recyclers in the state, but so far none of them wants in.