Just an update and FYI for anyone who has ever tried to purchase one of these from the local discount parts stores. They don't list the correct part for our vehicle. It comes up in their system as a 6 rib pulley, and it doesn't have the correct inner bearing shaft/spacer. In some cases it doesn't come up at all.

After a little research, I found the following compatible parts:
Dayco 89080 available at Advance Auto, Pepboys, and Autozone (alternate part #231115)
Gates 38091 available at Napa and Oreilly

All were right around $33-$35
Unfortunately for me, my local stores still didn't have them in stock, but yours may! I'm going to check with Mercedes and Chrysler tomorrow.