Matt, have you ever heard the expression "Beyond Economic Repair"? Thats what hapens when a vehicle reaches the point when it's cheaper to throw it away and get a new one than continue pouring money into it. OK, you can get lucky and like some on here you can enjoy years of cheap motoring from some old banger but the strong likelihood is that an old car will drain your resources faster than a trip to the bike shop.
If you're a good mechanic you stand a better chance of spotting that rare gem but most of the old cars out there have been sold for the simple reason that their owners were faced with a big repair bill and decided to get shot of them. Again, a good mechanic (with all the workshop facilities and plenty of free time) can keep an old car going using second-hand spares as we used to with our old Land Rover. It's satisfying and as near to ecologically sound as a car can ever be but it takes over your life and becomes a millstone around your neck.
Stick with bikes and public transport.