Insurance companies usually will try to pay the least amount of money for a car in a total write-off. The two methods that are characteristically used are; "average market value" or what it would cost to replace the car if you bought a similar vehicle locally, and "Blue Book" value based upon NADA or the Kelley Blue Book.
Check Kelley:
www.kbb.com
Get the Private party Sale value and the full Retail value. Add them together and divide by 2. That's what the average car is worth and the least they should pay you.
Check NADA:
www.nada.com
Do the same as above.
Check ebaY to see what a similar car recently sold for at auction (check completed items).
Check AutoTrader to see what they are selling for around the country and specifically where you live.
www.traderonline.com
And finally check your local newspaper to see if someone is selling one in your area, or with a local MB dealer to see what they have sold them for recently.
That should give you something to go on.
Also check to see if the shop, their insurance company, or your insurance company will provide you with a rental or loaner until you get a new car.
Good luck...