Yes, airbag is about £300, how much is the one in your image?
£150 for fitting/coding is not bad.
The wheel in the picture sells for £349.00. You can use the airbag & buttons from the orginal C55 wheel so total cost inc. coding should be (drum roll...) £500.
I have also been told that C55 wheels (without airbag & buttons) sell for around £150-£200 so it could be even cheaper!
If you currently have buttons, there should be no coding involved!
i know that paddleshift could only be swapped on the W211 post 2005, anything earlier there was a few electronic components which had to be swapped and was over £1500
drop an email to mbenznl, he should be able to answer