I would start to shy away from something with more than 20k... depending on how hard it was ridden/how well it has been maintained 20k is where a sport bike gets into issues or gets expensive with maintenance.. I had a 2002 yamaha yzf600r I bought at 19k, rode it till 24k and stripped out 2nd gear. which is a 1500 dollar fix on a 2000 bike.
if you know how to work on a bike it's way cheaper than that to fix, just takes time.