No,no,no..... not a ninja 250, a ninja 300!! mine is a blast!! well a 250 would be cheaper and they are a little fun too, but they are carbed, were as the 300 is fuel injected..... not sure if you can find any used 300's but look around, they surely should be about 3.5-4k, new they are 5.5k
Really low geared tho...both of them...and top speed is only about 95mph, but they are really fun in the twisties because they weigh next to nothing.
Or you could get a Yamaha WR250X and put some dual sport tires on it, as it only weighs like 285 lbs.
I've owned all three, and I would be torn between the 300 ninja and the WR250X...