The average price of regular gasoline in the U.S. has fallen 2 cents a gallon during the past two weeks.  Industry analyst Trilby Lundberg said Sunday a gallon of regular now costs $3.29 on average.  Gas is 30 cents a gallon cheaper than this time last year, as Lundberg says the price has dropped more than a nickel per gallon in the past month, but it’s unlikely to fall further unless crude oil prices plunge.  Of the cities surveyed in the lower 48 states, Billings, Montana, has the lowest price at $2.99 a gallon and San Diego has the highest price at $3.63.  The average in Illinois has risen to $3.38, that’s up a penny from the previous 2 weeks.  Diesel prices rose in the past two weeks by six cents to $3.95 per gallon.