Do an advanced search on Ebay and look at COMPLETED sales for the same model/age.......an opinion from someone here is just an opinion, but actual completed sales will tell you how much they ACTUALLY sell for
Cost of a new one with ABS in May 2006 was £9605 says my (slightly out of date) CAP Green Book So with 18,000 miles that bike would be around half now retail ie £4795
As Fanum says above completed sales is the thing to look at Are you buying,selling or trading it in?