That exact air bag module was used on 14 different Mercedes models; two of which are the SLK320 & SLK32.
IT WILL WORK ON THE CROSSFIRE!
The current price from Mercedes dealers is over $800.
SO, buy the module with part number 001 820 08 26 from ebay or a junk yard
If you have a friend or any one with a Mercedes program on their scan tool they will be able to clear your code and turn off the light in under 5 minutes.