If you want pricing for older cars, I recommend carsandbids.com. For example, here is a 2008 Audi RS4, that is currently bid to $18,000. It has 111,000 miles on it. https://carsandbids.com/auctions/3oj8pvR7/2008-audi-rs4-seda...

What an old car is worth depends on many factors, but age is not the most important one. The average age of passenger cars on the road in the U.S. is 14 years old -- I think 14.5 years now. I don't think we have data on average appraised value of passenger cars on the road, but I would guess it would be in the range of 10-15K.