6-7 thousand if you are buying an G-35 from Infiniti but not a 16,000 car. You probably have to only make a down payment of 1-2 thousand.
Oops, sorry. I'm used to used cars and a 2-3 year loan. Yeah, the standard 5-year loan for a new car would have a lower down payment than that. xD

Be careful about classifieds or auctions or crap like that. Unlike used car dealerships, there's not much guarantee about the condition of the car and no warranties or anything. Unless you're really experience and/or know a mechanic, it's probably best to stick to dealerships.