creeking - 7:22 pm on Feb 7, 2013 (gmt 0)
it might be unsophisticated solution, but can you reuse the car page URLs?
like using page001.html through page100.html for car ads. when a car on page100 is sold, it is replaced with another car on that same page100.html.
also consider adding a "no archive" meta tag to your car pages.