Im thinking on going on a roadtrip this sommer. And Im thinking of buying a car like an older cadillac Eldorado, Deville or Seville
1.How much do I have to pay to get a "reliable" one?
and how honest are the average carsales man? or is it better to buy it from a private saler
2.How much does the insurance and regestation cost if am 20, not from the us and how long time does it take?
Two websites that will give you an idea of prices for used cars are: edmunds.com and kbb.com
Those are nice cars but gas could get expensive if you're traveling far.
There are a lot of jokes about "honest" car salesmen. You are always taking your chances whether you buy from a dealer or a private person. Many people have a good mechanic check out the car for a nominal fee before purchasing to try to avoid lemons.
I have no idea how someone who is not a resident of the US can buy a car. There are other threads on this issue. YOu might do a search here and you may find your answer.