I just went through this whole ordeal myself with my '91 300E. I ALMOST went with the Sportline suspension but since my E had 200,000 miles on it, I didn't think it would be worth it.
My shocks were sagging so bad the car had a lowered look to it -- looked really nice so I decided I wanted to keep that look.
What I did was purchased Bilstein comforts all the way around and 4 OEM springs. The cost shipped was about $500 with 2 new front strut mounts, strut boots,strut bumper stops, and sping pads.
I personally put the shocks/struts on (VERY easy job) but had trouble compressing the springs because they were sagging so bad. (I was using a spring compressor that I bought from JC Whitney, that compresses inside the spring -- when the coils are real close together like mine were, it's almost impossible to work inside of there and compress it properly -- I needed the "plate" compressor that most MB shops use and that you can rent for a measly $90 from Performance Products)
So I had Pep Boys replace the springs for a very decent price.
To get the lowered look, I switched from 3 bump spring pads up front, down to 2, and from 2 down to 1 in the rear.
Rides just like new now, and it was the best $600 I spent on my E yet. Suspension wears so gradually over time that you don't realize how far it has worn until you find your car bottoming out over trivial bumps. It took about 3 months for the new suspension to wear/settle in and now it rides like a charm.