I have a 200 and once got 69 miles including reserve. Most of the time around 40 to 50 before I hit reserve. But it all depends on how and where your riding.
I've got a 97 KDX200 and get about the same... I run Motorex Cross Power 2T (fully synthetic) at about 50:1
That kind of millage is pretty much flat strap through mud, forest and hilly trails. I don't know what it'd be like on the open road as I use the KLR650 for that... once the KDX's feet hit the deck it's ridden the way it should be... like a 2 stroke!
Anywhere from 35-50 miles before hitting reserve on the trail. I dual sport it, and if I keep it around 45-50 mph cruising in 6th I can get 85+ miles! My buddy has a simular KDX 200 and was telling me he could get over 80 miles to a tank, I didn't believe him till I did some more riding on mine.