Also, not all 12V fans are created equal. Since you're talking about using the fan for cooling, you have to assume long run times and 100% duty cycle.
A 12v car radiator fan or heater blower isn't going to cut it. These are generally brushed motors with sealed plain bearings. They're designed for a definite lifespan, which is a long time on a car, but the car application has, at most, a 30% duty cycle.
Now you can go with a bunch of computer-grade 12v muffin fans, but they also make 120vac muffin fans, which saves you from needing a second power source to run the fans. These are all available as pretty cheap surplus.
If you need more airflow, comair/rotron makes (much) bigger 120v computer fans. The Patriot models move serious air. Of course, they're also pretty noisy. If low noise is your primary concern, you may end up working with the 12v muffin fans again, and run them at 7-10v.
If it were my application, I'd design around surplus 120v muffin fans because my listeroid is a 120v generator. One less conversion step, one less thing to go wrong, and the muffin fans are pretty efficient, so not much energy is lost to moving the air around.
Of course, if you want to get really slick, you could plumb up an exhaust extractor and use that to pull air over the radiator...