Depends on the car and how well you check it out, a small SUV should be fine as long as it has no undercarriage damage from being misused. Most semi reasonable people don't rent a SantaFe or a Soul or a Murano to offroad or autocross, they use them like a minivan. Those are all probably a good deal for the right price. I'd personally would not buy a rental company performance car or vehicle, there is too high a chance a previous renter decided to live out their Two Lane Blacktop inspired fantasy. And the damage may not be visally or mechanically evident for thousands of miles to come.