"Do the coupes always come with the Sportline suspension? I presume it was an option.
If I decided to upgrade a sedan or coupe to that suspension, what kind of money would I be looking at?"

No. Most coupes did not. In fact, a vehicle with factory Sportline Option (in great condition/low miles, etc.) may be tough to find.

If you are a DIY, you could swing the conversion for $1,200-$1,500, plus the cost of a good alignment. The only real difference you won't get is the quicker-ratio steering, badges, etc.

I am in the process myself of having this done.....my budget will be in the neighborhood of $2K. If you are considering BMW vs. Mercedes, this is a small price to pay.

Again, for $20K you can get a cherry car and still have the cash to upgrade the suspension. Plus, you'll own a car that will provide you with all the safety, engineering, performance and longevity that MB's are famous for.

As for the 94 and up cars (E320) only having the Sportline Option, read the information under the "featured cars" section. Any of the 124 coupes or sedans from 92-95 could be ordered with Sportline as a factory option. But, this does not preclude earlier model year 124's from benefitting from upgrading to this level of performance.

If tighter handling is the only thing keeping you on the fence between Mercedes and BMW, this may prove to be an alternative for you.

This topic is very subjective, though. What may be great for me may not work at all for you (I had a lengthy discussion with an MB tech recently as to what his favorite car he ever owned was; he said his 1993 300E (with factory sportline), even over his 500E! - I thought he was nuts...)

See if there is a car in your area you can test drive with Sportline. The only way you'll know for yourself is to compare.

Good luck in your search!