I would actually not rule out a car with some rust. You just have to consider the cost of properly repairing it and whether having either new panels or new sheet metal makes your car unloveable versus the value of the rust as a dicker point on price.

I got mine with some rust at the p. side rear wheel well. I was able to negotiate down significantly (the car had all records and the window sticker, but it just wasn't a trophy, it was a tool). The replacement of the part was less than the savings, so I don't see it as a detraction. If you get a PPI and the car is in mechanical shape, use an estimate of repair to get the cost down. I'm not an old pro at this though, just beginner's luck, but for what its worth.