Fuel mileage will be dependant on traffice conditions like stop and go traffic or wide open road where you don't have to worry about slowing down and speeding up. There following are based on 2011 models:
Yamaha Enticer 125: City 36 kmpl / Highway 59 kmpl
Yamaha v star 250: 33 km/l average
Suzuki Gz 250: 82 mpg average
Hope it helps, good luck!