There have been some issues regarding the CVT transmission, but the car is likely not old enough to have an expired warranty. My bet is that the owner did something to violate the warranty. Take a look at the nissan website and make sure you know what to expect. The other thing is that the cube has only been in the US for a few months.
Second of all, the absolute base model cube is only about $15k new. I don't think it gets much cheaper than that.