I got a key for my 300E about a year and a half ago. I think I paid $22 plus tax from a dealer in Scottsdale, AZ. The only bad part was that I had to drive all the way across the Valley twice. Once to order and once to pick it up.

The good news is that they are close to a Cheesecake Factory. Key=$22. Two lunches at the Cheesecake Factory=$80.