Some shops fit them for free if you buy the pickups from them. My first set of BKP's were installed by the shop I bought them from as a freebie.
Not everywhere does it though, and if you've already bought the pickups, they will charge you for it. Last time I asked, one shop nearby charged around £25 per pickup...
A great incentive to learn how to solder pickups (and do set-ups as well!).