Lost every C-Class key?
With no key left for a 2001 to 2013 C-Class, the work still happens where the car sits. We usually pull the electronic ignition switch, read its stored key data on the bench, program a replacement from it and reinstall the switch, with the lost keys blocked from starting the car. It totals $389, or $329 plus $60. Keep your ID and the C-Class registration or title nearby.
For a C-Class from 2015 on with no key, what you hear up front is that Mercedes makes the replacement for your VIN and a dealer orders it. Take proof of ownership and a photo ID to the service desk so the order goes in once, and allow for shipping time from Mercedes. A 2014 gets the VIN check before either answer.