The SRS light came on, on 2004 Mercedes-Benz S430

what does it cost to troubleshoot and repair?
How much is the electroinc module that controls this?

Asked by for the 2004 Mercedes-Benz S430
Don't do a hearth surgery immediately.
The SRS system has to be diagnosed possibly with SDS, and repair it accordingly.
There might be nothing wrong with the system, only an interference issue. You need a MB specialty shop who has the SDS.
Read this:

To properly diagnose this issue, please follow the SRS fault tree in Star Diagnosis (SDS). This fault tree can be found in a quick test by selecting the stored DTC. If no faults are found, the cause could be a memory card with a transponder chip has been placed on the passenger seat. Company ID cards, notebook computers, PDAs, and other electronic equipment may contain such memory cards that cause interference with the Baby Smart(TM) transponder. This interference can be interpreted as a fault by the SRS control unit. This condition may be difficult to duplicate in the workshop. Please alert the customer not to place items containing memory cards on the passenger seat. Replacement of components will not remedy the situation.
Note: The interference from electronic components is an outside influence and not a manufacturing defect and therefore cannot be claimed under warranty.