6500 hours is getting up there but not terrible, also depends on how much you're going to use it and how it's been maintained.. It's got a Cummins 12V 5.9L engine, so I wouldn't worry too much about that part, even if it dies, there's tons of them around.. I'd be much more concerned about the 4wd system, front hubs, u joints, transmission, brakes and tires.. all that stuff gets expensive really quick... Good used engine can be had for $1500 now.
On the transmission, it's got an over/underdrive in each gear, and that part is probably an electric over hydraulic clutch... If those are worn, that's going to be an expensive repair bill.. Make sure that part works, I'd recommend hitching something heavy onto it and ensuring the powershift doesn't lag or slip
Does it have a loader and cab? The loader in particular would be the thing that puts the value onto the tractor, without it, I wouldn't pay that kind of money for it