I done mine and really weren't too sure what I was doing on my K11.
I'd hazard a guess a garage would charge around £30-40 per spring.
Going by the K11 they are easy to do, rears is a case of loosening the shocks, jacking it up, putting some pressure on the rear drum and springs can easily be pulled out/put in.
It's not a hard job on the fronts but you will require some spring compressors.
