FWIW - I just bought a 2001 KDX 220 and I LOVE it
I paid just under 2K, and it is bone stock. This page (and Canadian Dave's) are HUGE sources of great info - I'm slowly beginning to apply a few upgrades to get a little more out of the bike, but even stock it is a sweet machine.
In California, the biggest advantage of a 2002 or older KDX 200/220 (over the newer ones) is that it is green sticker legal - the 2003 and up are not. This may or may not be an issue where you ride, but I suspect we're all going to have to be thinking about environmental impact issues in years to come, regardless of where you live.
I don't remember if you push the tripmeter button, or turn it, but it should be very obvious if it is a tripmeter - odometers (by law!) aren't supposed to be resettable (at least not easily...) - so don't be afraid to play with any buttons/knobs you see.
I'm a newbie here - there are more knowledgable people out there, but for 50% of the cost of a new one, I do not think you'd be disappointed with a used bike if the guy take any kind of care of it. That 2K saved will buy a LOT of upgrades...
Jonathan