MAFS SENSOR?

I DRIVE A 2001 NISSAN TINO 2 LITRE ESTATE WITH ONLY 36,000 MILES ON THE CLOCK. MY CAR KEEPS CUTTING OUT IN TRAFFIC AND NISSAN HAVE TOLD ME IT WILL COST £500 TO REPLACE THE MAFS SENSOR, IS THIS CORRECT, AND IS THERE AN CHEAPER WAY TO REPLACE THIS SENSOR, HOW MUCH DOES IT COST TO BUY ?
Best Mike London.