Look it up on the Autotrader. You can set your criteria, save the search and every time a car that meets your requirements is advertised you will get an email notification with a link to the ad.
www.autotrader.com
Here's a real nice one. http://www.autotrader.com/fyc/vdp.jsp?ct=p&car_id=247006040&dealer_id=62854867&car_year=2005&model=MUST&num_records=25&systime=&make2=&start_year=2005&keywordsfyc=&keywordsfyc=&keywordsrep=&keywordsrep=&engine=6+Cylinder&certified=&body_code=0&fuel=&awsp=false&search_type=both&distance=0&marketZipError=false&search_lang=en&make=FORD&keywords_display=&color=&page_location=findacar%3A%3Aispsearchform&min_price=100&drive=&default_sort=priceASC&max_mileage=75000&style_flag=1&sort_type=priceASC&address=30066&advanced=y&end_year=2005&doors=&transmission=Automatic&max_price=10000&cardist=1917