My dad bought a 1971 Buick Centurion off Ebay, and went all the way out to New Jersey to get it. It was a great deal, probably less than $10,000, and he is very satisfied with the car.
We also found my mom's car on Ebay, but instead of buying it online, my parents flew down to Missouri to buy the car from the dealer, and drove it home. This car was brand new, and $10,000 below MSRP I think. Incredible Savings.
If you know how to buy stuff off Ebay, and are willing to travel across the country, then yes, you can get really good deals on cars.