Hi, I've got some problems with my rear shocks too. Bad knocking from the back end. I was looking at scoobyworld.co.uk and they do a pair of rear KYB shocks for £265.
3 hours to replace 1 rear shock is a bit (pardon the pun) shocking. rear wheel off, rear seat out and your right in about. 3 nuts on the top of the strut and 2 bolt at the bottom, unclip the brake flexi and that's the rear strut out.