Dear customer I apologize for the delay in communicating with you the time zone affects me a little.
Dear customer, first I want to indicate is that the error codes that you are presenting are related to failures in the exhaust system, in the exhaust of your Mercedes. There are some sensors responsible for measuring the amount of pollutants that come out of the exhaust, these sensors are the sensors that are throwing you the diagnostic equipment, normally the corrections of this failure lead to verification of the systems in a deeper way because what is happening is that the sensors of this exhaust are detecting a mixture not stoichiometric in the cylinders ( I.e that there is not an equal amount of fuel with an equal amount of air as it should be), this means that you have to verify the entire air intake system and the entire fuel injection system to be able to solve this fault which becomes tedious.
For this, first a monitoring is done and some tests to the exhaust sensors to corroborate that they are not defective and that the signals of the error codes is throwing them by problems in the sensor but not problems in the mixture.
This is why this review is always tend to be a little deep because it does not rule out the sensor and then proceeds to verify if there are problems either in the air intake or fuel injection.
Now dear customer, the technicians of just answer are in different parts of the world not only in United Kingdom, I for example am currently outside the United Kingdom and could not personally help you, therefore if you tell me your location, i could try to locate a garage that can help you with the diagnosis of this problem that you present, but the truth the check of the sensor, with the check of the fuel rail and air intake cost range is between 100 to 200 pounds, this is why I think that the price you are being given in the Mercedes is within the range.