About £350 plus fitting less any discount you can negotiate 
Price of the parts listed here:
http://www.bmw-motorrad.co.uk/media/pdf/R-1200-GS.pdf
My dealer wanted £190 labour
Did a deal as part of ordering the new bike and got them all in for under £300 fitted which is still not cheap!!
Price of the parts listed here:
http://www.bmw-motorrad.co.uk/media/pdf/R-1200-GS.pdf
My dealer wanted £190 labour
Did a deal as part of ordering the new bike and got them all in for under £300 fitted which is still not cheap!!