The average Dutch/German 1991 300CE-24 should be worth between 7000-10.000US$ (depends on the state of the car). Do you have a 12 or 24 valve?
If the insurance company pays you the damage that is estimated by the MB dealer and you get paid without a bill of that MB dealer, I would let the damage be repaired by somebody independent or I would do it myself.
In the Netherlands we have insurance companies who pay for damage after it is repaired and they get the bill and we have insurance companies that pay the damage that is estimated without seeing the repair bill at all.
So to determine where to repair the car, you would need to know under what conditions the insurance company pays...
with a minor 600+k