Check out the Kelley Blue Book online.
There are likely other good sources of info as well. If you're buying from a dealer(not just MB), you can bet the asking price will be more. Good luck.
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.