DETROIT (WTVB) - Motorists are still getting a break at the pump, but they may not be for long.  The latest numbers from the Lundberg Survey show the national average price of self-serve regular gas at $3.41 a gallon as of last Friday, down 7 cents over the last two weeks.  But she says world demand is up, crude prices are rising, and soon gas prices will also rise. Gas Buddy.com shows gas prices in Michigan coming in at about $3.50 a gallon, about a dime higher than the national average. Prices range from as low as $3.20 in Niles to $3.80 in Detroit.