For comparison's sake, my 300TE resonator costs around $250 (with the dealer's MBCA discount of 15%) and nearly $300 for the muffler. I replaced the resonator about three years ago, so I'm not thrilled with the longevity. Then again, I'm in the northeast.
Both my muffler & resonator have begun to leak a bit, so both get tossed tomorrow in favor of a fully stainless setup from Time Valve for $650.
For an extra $100, how can you go wrong? A large piece of their business is OE retrofits for Mercedes, so I'm confident it'll fit fine.
All the best, Michael