Buy the best car you can afford!!! Stay away from rotted cars ! Rot is almost always worse than it looks. Better of buying a car from the south or out west since their climates are drier and they dont get the snow or salt the northern cars do.
When i buy a car up here in the rusty northeast 1 st thing i do is look at the doors on the bottom and that is a good indicator for the rest of the car usually rust wise, make sure they have not already been bondoed up and are thick. A really thin refrigerator magnet helps spot bondo you dont want a strong magnet the thinner the better! If you have a strong magnet it could stick through the bondo.
Check the lip of the trunk lid on the inside behind the moulding to look for rust blisters.
Look at the frame rails for rot. Look to see how bad things are under there! Is there new looking brake lines,fuel lines tranny lines? All of these can and do rot out !
How are the bumper fillers?
Is the dashpad split? These take a whole bunch of time to change and cost $ to buy another
horn button cracked? Steering wheel leather shot?
Are the upper door panels shot? How are all the seats? I have seen several back seats explode from the suns uv rays.
Yes the quarter rot out, rockers and floors do as well. T top cars the roof can rot out too!
I have even seen a steel front bumper supprt rotted!!! I have seen many rear bumpers and their steel or alumnum supprts both rotted.
Also do yourself a favor and only buy a 86-87 because a bunch of the 84-85 guys usually end up converting their cars over to intercooled eventually anyway.
Cars with original radios often have not had their wiring butchered. Also look for cars without a aftermarket alarm since those cars also have their wiring butchered too!
These are a few things i can think of quick. Also take somebody that is more knowledgeable than you along to help with the decision making because these cars can become frustrating money pits quick.
The trannys are almost always another problem area and whatever you do make sure to get a vendor from the board to rebuild your tranny should the time come otherwise you will be doing it twice!!! Ask around on here there probably a builder in your area from on here. I have personally broken about 10 of these trannys.
Also make sure the 8.5 rear that is suppose to be in the car actually is since i have seen many cars where it was pulled out! I have personally bought 2 diffrent 85 gn's and a 87 turbo t limited and the rears were replaced with useless 7.5 rears. I knew this a head of time and used it negotiating price. But these rears are often worth nearly $1000.
I also prefer cars with their original drivetrains and unrebuilt engines.
YES EVERYTHING IS REPAIRABLE IN THIS WORLD BUT IT ALWAYS ISNT WORTH THE TROUBLE.