Dean,
Your first post is requesting info on when should a rear shock be changed. Your second post is now asking for a recommendation on where to take your bike but have not said what for. A service, a clean, a new shock, an MOT, a chain........ what for?
Can't help you unless you are specific. Prices vary enormously depending on the bike, what you want it to do and how much you're willing to pay for a brand name. I have spent a couple of hundred on one bike and well over a grand for another. There's lots of choice out there.
p.s I'm a west Londoner too!
