I think ball joints and struts should be low on your list for things to worry about.
Ball joints very rarely wear out on this car, and original Bilstein struts are extremely long-lived. So long, in fact, that they aren't even on a scheduled replacement interval.
They should last at least 200,000 miles before they may need replacement, and they are not that expensive, especially if you do it yourself.
The front has struts and the rear has shocks. The rear shocks, in particular, are cheap.
The three expensive things that you should be worrying about are:
1. transmission: 150,000 - 200,000 miles is an average life of an automatic tramsmission. About $2,500 for a rebuild.
2. a/c - the weak point on these a/c systems is the evaporator. The original ones have a tendency to leak. The part itself is not that expensive, but the labor will kill you. We joke that the engineers designed the whole car around the evaporator. It is buried underneath the dash, and everything in the interior of the car in front of the front seats needs to be removed to access it. The shop labor time is 17.5 hours if I remember. You'll have to budget about $2,000 parts and labor for replacement.
3. M103 engines are prone to valve guide wear, as well as oil leaks at the head gasket. Either of these require removal of the head. Budget $1,200.
I wouldn't let any of the above scare you away from buying the car. You just should know what might happen within your ownership experience should you buy the car.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".