Put your registration into Eurocarparts and enter MBCLUB30 as a discount code and get 30% off. They were listing two MAF'units, one Bosch at £180 before discount and a cheaper one at circa £50.
Changing the MAF unit is very simple, usually two jubilee clips hold it in place and an there is electrical connector to unplug and put back.
OK, no idea on that one as I have never seen the supercharged engine. As for the MAF, do it yourself or at least buy it yourself as £126 Vs £216 is a better option.