Its cheap because parts support is a bit of a problem unless you don't mind buying direct from Wolf Hobbies. Also since its not just because its old, its because the original design had some flaws. Over the generations where it has been updated, the flaws were remedied and those new generations are the ones that are worth more. The problem with getting an older chassis that needs updating is that eventhough it may be cheap, if you add all the parts needed to update the chassis, it will cost you more than what it would cost if you were to buy the newer updated one, that has all the problems remedied.
I know this because I got a G4C, back when it was really new and really cheap. Two major problems, steering and placement of the electrics. I want you to know, I've spent more money in parts than I have in the original kit and it still hasn't worked for me. The engine compartment is tight and is difficult to install and remove the engine from its mounts. Also you, need to invest in a low profile steering servo and a micro receiver in order for the electrics placement to workout because it is TIGHT! At this point, I've just about given up and decided to move on.
I'm currently running an MTX-3. Its an old car but not that old. It still can handle quite well, but I'm finding it a bit difficult to find parts for it. However according to Mugen USA, there's still plenty of parts for it.
I plan on getting a newer chassis soon. Believe me, you do get what you pay for.