NEW YORK MAYOR David Dinkins says the $11,500 figure Newsweek magazine cited as the city's price tag for a hand-carved headboard delivered to the mayoral Gracie Mansion is "absolutely ridiculous." Dinkins spokesman Albert Scardino, disputed the $11,500 cost on Sunday, saying materials for the headboard cost $1,400 and that labor costs should add up to an additional "few hundred dollars at most" . . . SOME 3,000 TEACHERS in New Orleans voted to end their 3-week-old strike immediately and accept a contract offering 7 percent pay raises over the next three years . . .