Stock shocks can be had for £50 ish, so had a look on ebay and found one going for £30 atm.
http://www.ebay.co.uk/itm/Yamaha-FZS1000...1c46d1d406
The other option if you are able to have the bike of the road for a bit is to get your shock rebuilt -
- http://www.maxtonsuspension.co.uk/files/enquiries.htm
- http://www.falconshockabsorbers.co.uk/repair001.htm
- http://firefoxracing.co.uk/rear-shock-servicing
- https://www.google.co.uk/search?q=motorc...o.uk+-.com
http://www.ebay.co.uk/itm/Yamaha-FZS1000...1c46d1d406
The other option if you are able to have the bike of the road for a bit is to get your shock rebuilt -
- http://www.maxtonsuspension.co.uk/files/enquiries.htm
- http://www.falconshockabsorbers.co.uk/repair001.htm
- http://firefoxracing.co.uk/rear-shock-servicing
- https://www.google.co.uk/search?q=motorc...o.uk+-.com