Let us start with ease of obtaining. Obviously newer car parts will be easier to get than older ones. A friend of mine still has a 1975 Pontiac Lemans. To obtain parts for this car he has to literally go to junk yards and even online. No new car dealers keep parts beyond 10 years or so and even auto parts stores limit their inventory to cars under 20 years. A 30 year old vehicle is almost impossible to find parts for. Plus, if you can find the part, depending on where you get it, the cost could be anywhere from 20 to 100% over the original part cost.