What kind of car do you want? With Alfa's the most common one's out there are Giulietta/Giulia Spider's and GTV's. When looking for a car don't just buy what looks clean, it's better to buy a PROVEN car before the best looking one, but this does not mean to go buy junk. Once you find a car, try to speak with people who compete against the car and see what they tell you. Don't always rely on what the owner tells you because of course he is gonna tell you he has the fastest car out there.
When looking at the car, you wanna see what you are paying for.
-Does is have a panhard rod, close ratio transmission, built motor?
-How many hours are on the car and motor? who worked on it and how is the quality of upkeep?
-Ask to see logbooks and result sheets.
-Does the car have any history? This could add to the value of the car because it would qualify for some special events.
-Does the car meet the required rules for you local vintage club? I know of some cars out here on the west coast that would never be let off a trailer at some east coast events where the rules stick to true "vintage"racing.