I picked up a used one 2 years ago as my first motorcycle. Put about 9,000 miles on with only having a solid 4-5 months of good riding weather between 2 years.
I found a 92 with about 5K miles for just over a thousand bucks. It's been a great bike, never broken down or left me stranded. I really can't say enough good things about the 250 for any rider. Great MPG and cheap insurance. Parts are easy to find and relativly cheap. I don't know how much research you've put into the 250, but feel free to ask my anything here or via PM.
www.ninja250.net is a great site with an exhaustive FAQ and a reliable messageboard.
And don't forget about the MSF course, you'll learn a lot.

If you need a testament as to how much I enjoy the 250, check this photo out:
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