It's a fixed rate to open it up and bring it up to spec with the latest firmware and board fixes. I think my GNS430W a while ago was $1800. You have to call Garmin and get and RMA and current pricing. My GNS430 had the vertical guidance board fail. They replaced that, upgraded the software to the latest, and implemented a patch on the motherboard that corrected some issue with the early generation circuit design. Works like a champ.
Turnaround is pretty quick, and you can rent a slide-in loaner for a reasonable price if necessary. (Interestingly my loaner screen failed and had to be replaced.)