Well, for a really good car be prepared to spend $5,000 and above, for an average car, $2500-$3500.00. But even if the car is "really good" its going to need work to be perfect. If you have a car with 130k, its going to need work, typically if it hasn't already been done. Things like suspensions, timing chains and head gaskets will probably need fixing, not to mention A/C and vacuum tid bits. Things can get more expensive as the cars age, but if you buy it with records, you know what you are getting.

I'm going to go out on a limb here but, these are not cheap cars to own. To maintain them correctly, they need money. Sure, they are much better than other 20 year old cars, but they are 20 year old cars! They are not going to be perfect. It all depends on the level at which you want to own and drive these cars. If you want a "like-new, drive across the country" 300D, it can be a $20,000 investment over the course of 5 years. I don't care how much work you can do yourself, there's a considerable investment of tools and time to DIY a Mercedes correctly. You can also drive a beater for a few thousand dollars and nickel and dime it till it stops, its going to be a very long time before it stops...

As per the 85 Cali version, I would stay away, if you can find an 85 Federal Version, great! But I don't know how legal it is. The 83 is a sold year, I would own an 83. But for some strange reason, as stupid as it sounds I'm not a fan of 82s and 84s. 82s for they were the first year, not that there is anything too wrong with them, but an 85mph speedo? and being the first year, they have minor niggles- all can be updated and fixed over time. And the 84, while an awsome car is just a year short of being an 85, my favorite... So, I'd rather wait for an 85 if I didn't live in California. But outside of my demented world, there is nothing wrong with ANY year w123 300D.

Rule is, no matter how nice a car is, its a matter of time before it breaks or needs attention. The few thousand more for a super clean car is just buying time really. Of course, things like rare options and colors go with the choice as well.