Can't help with the garage but I would fit the Gruppe M yourself, it's pretty straightforward and you'll save yourself the labour cost. The instructions are slightly dodgy English but following the pictures it's easy really. I'd happily help you through PM if your unsure.
Just got a price back of £249 for springs fitted, Gruppe M filter fitted and HUNTER 3d Alignment from Aaron at "A reeve" - Aaron discounted for me being a forum member.