I haven't seen a sign of rust on any body rust on an IS200. When I saw the underside of my 1999 model on a ramp, it looked pretty much like new (other than the exhaust). The OEM wheels are highly prone to corrosion though, so you shouldn't be too worried about badly corroded wheels (other than perhaps building in a refurb to your budget).
I'd say that with it being a buyers market at the moment, you should be able to choose your favourite spec level, your favourite colour, and then look at cars that match those together with your budget, until you get one that feels right (I don't mean in terms of handling, I just mean it seems like an honest car).
Check when the cam belt has been changed. Lexus originally recommended this was at 100K miles or 10 years, but they changed this to 60K miles or 6 years. One member here has recently had to get quite a few new parts for his engine after his cam belt snapped.