Triple A says the nationwide average price for a gallon of self serve regular is now under the 4-dollar mark.  Could Fairfield County be far behind?  Many experts think we will see another 15 to 20 cent drop by mid September. Regular prices over the weekend ranged from 4.39 in Greenwich and Darien to 4.09 at one Norwalk station.  Motorists should continue to shop around.  Warehouse club members can also usually save another 10 to 15 cents per gallon.  Some clubs in New Haven County are already as low as 3.95 per gallon.