any nissan mechanics?

[losixxx]

Hi
my mums just been quoted £700+ for a replacement throttle body and air flow meter on an x plate 998cc nissan micra, however the mechanic said you can just change the air flow meter which i can get for £45,
my local motorfactors have said i may need this calebrated and they only sell the complete throttle body/air flow together...
can the air flow meter just be replaced one for one or will it need calebrating? as the nissan mechanic didn't mention anything about this
thanks