Well, that 2,500 pounds sets your lower limit.
If it helps, I bought a 2011 in 2012 from a dealer. It had 300 miles and was in the US where KLRs and parts are like fleas on a dog. I paid about $4,700 plus taxes and fees for a bike that would have sold new for around $6,300 plus taxes and fees. That is about 75% of new cost.
Yours is four years older than mine was and located where they are not sold/serviced. My really loose guess is that 45 to 50% of its new cost before tax would be the top of the range.