...be prepared to spend ... on "here and there" items, like worn out levers/perches, and footpegs/springs/pins...and don't be surprised if you spend several hundred more than that, on things to "personalize" it to your liking...
Gold star used KX500 purchase advice if there ever was any.
Proof: In the past year and a half I picked up a "great condition, fresh top end, good suspension, blah blah blah" KX500 for $1700, rode it for around 8 hours, came to find out it had not only flaws but fatal flaws. Long story short I am finally getting to the point of ready to receive the bottom end back from a local builder in the coming weeks and am now starting to deal with the trivial stuff. My $1700 "great condition" bike is gonna cost me close to $4000 by the time it is track ready.
Some off the top of my head used KX500 advice is this: Inspect the frame with due diligence not only for structural issues but also bent/broken mounts, stripped threads and previous repairs, check the steering stops on fork & frame, check the radiators for warpage, damage or repairs, look for burn marks on the underside of the gas tank over the muffler, check rear suspension play, check for wheel axle play, pull the muffler & inspect cylinder/piston, pull the oil drain plug & check the case threads, pull the rotor & inspect the crank keyway just to be safe.
Here is why "pull the rotor" before purchasing "great condition" KX500:
http://www.kxriders.com/forums/index.php/topic,15209.0.htmlEven if the bike turns into a nightmare, $1500 is still a good place to start for a KX500 that starts, runs & isn't a total pile o crap. Consider that a excellent KX500 is probably worth $4-5000, good condition KX500 around $3-4000, mechanically good needs minor here & there around $2-3000 leaves running fixxer uppers between $1-2000 with major projects, parts bikes and basket cases under $1000. So at $1500 the bike you are looking at considering its condition is priced in the right ballpark at least.
Good luck with your purchase. Keep us posted.