The dealer will be using the worst-case labour estimates in the system for disassembly, diagnosis, reassembly and perhaps an allowance for repair, so that their risk is covered, ie you’ve agreed to that amount before they start.
It could end up being much less, and there could be no cost at all if it’s covered by the warranty. Assuming you have purchased the Mercedes-Benz extended warranty then “Sunroof cables” are excluded, and hence the possibility that the warranty may not cover the repair.