Before you start
Before you start, determine, of course, what kind of car you want. Using the make, model and year, use the Kelley blue book to determine what the market value of the car is, depending on its condition. This will give you a base figure to work with when it comes to deciding what you should pay for a car.
Next, decide what you are going to use the car for. If you're going to use the car every day just for transportation, you probably don't need one in mint condition, and you'll be able to pay less. In addition, if part of the reason you're buying the car is so that you can work on it and bring it back to its original condition and restore it, that's another reason you won't need a perfect car. If you simply collect cars or you just want one that's in mint condition and you don't have any intention of trying to fix it up yourself, then you'll pay significantly more for a "good" to "mint condition" car.
Know what the problem areas are going to be
Just about every make, model and year of car has specific problems particular to it. In other words, there's just about no car model out there that gets away scot-free. So research the car model you want and make sure you know what problems you should be expecting. This will help you determine not just how expensive a car is going to be to buy, but how expensive it will be to keep. Again, this isn't necessarily going to be something you're particularly worried about if you want the car for itself as a showpiece and not for daily use, but it's still something you should know. It also may affect how much you pay for the car.
Classic car trader clubs
There are lots of clubs available based upon specific classic cars for people who have owned the type of vehicle you want. Joining one of these clubs (many of which exist online now) will help you know what you can buy and what you should stay away from.
Once you find the car you think you want
Remember that just as with any type of car purchase, previous owners can "pretty up" cars so that they look much better than they really are. Have a car appraiser look at the car before you buy. They'll probably be able to tell you whether or not the car's been in an accident, whether the engine is in good shape, whether the transmission is shot, and so on. If any of these things are true, this will lessen the value of the vehicle and therefore the price you pay. And of course, you may not want the vehicle at all once you find these things out.
Pull a used vehicle history report
You should be able to pull a used vehicle history report using the car's vehicle identification number to determine whether or not anything is wrong with it other than what you have been told. It will also tell you whether or not the car has been stolen (which happens sometimes) and how many people have owned it previously.
Knowing your way around the classic car trader environment will help you get the perfect classic car you want, based upon what you want to use it for. You shouldn't have to pay more for the car you want than it's worth; armed with a few simple facts, you won't have to.