I always figure that any used car over 5 or so years old, plan on putting another $1000.00 into. That's parts, doing your own work, not taking to a shop. That's from a few decades of life experience.
In these old ones, it will vary widely based on how well the previous owner maintained it.
BUT the $ is not the main challenge. The parts availability is. I like these models, I run 2 of them. I occasionally have people asking about them, "oh, I remember mine" etc. So surprised to see one here in CT. I have 2 partly because if one develops a problem, I have the other to get around in while I wait for / make / recondition parts. I don't have to get emissions tested any more. I don't want air bags. I have made or bought all of the special tools. I know the quirks to watch and work around. I have engine and drive line parts from several that I retired due to the body rusting away. I have factory service manuals that I bought from a dealer, way back when I got the first couple. You will want a set but you have to search for online scans, or watch ebay, etc.
As much as I like them for me, I want to be sure that someone new knows the challenges involved in maintaining one. It is going to be difficult finding a mechanic that really knows these old ones also, so plan on being your own mechanic, or spending LOTS of cash.
Any hose, seal, gasket older than 10 years probably should be replaced. Radiator condition. #1 way to blow head gaskets is to neglect the cooling system. Radiator must be in very good to new condition. All SEVEN cooling system hoses should be no older than 10 years. Any EA82 I've ever owned needed a reseal from the head gaskets up by 10 years old / 150K miles if for no other reason than oil leaking everywhere. Timing belts every 50K miles if you want to be on the higher side of reliability. Alternators wear out a brush at about 150K miles like clockwork. Don't use cheap parts.
If you have time, space, and other transport for down time, great, we'll help. If you need one reliable car, have no shop, no garage, and can't miss a day or 2 from work, not the best idea....