For a complex suspension system like that, $2200 seems a reasonable price for that job to me. For the front strut with the active suspension option I’m seeing $1500 for the part, and 3.5 hours labor. That’s just for replacing one side front strut, not both. You’re getting a bit of a deal on the part, $100 off, but being charged a little more in labor than I’d expect, on the order of $175 / hour. If that’s all they’re doing, maybe that’s just their standard labor rate. Rich Bavarian air and all. But if they are also replacing other stuff, overall sounds like a completely reasonable price. Even a bargain. It’s the price Mercedes owner’s with the active suspension option pay for the ride quality.
You could possibly switch to the non-active suspension option. Ask about that. You’d have to do that on both sides of course, but the parts price for the non-active strut is only $250 ea. Not sure if that’s possible to do only on the front though, as the back has a self-leveling option from what I can tell too. So you might have to swap the back parts out too. The back non-self leveling strut is $200 ea.