I'm sorry to say this, but welcome to the repair center. You really have no choice at this point, it's beyond what you can do and what I can think of. It's efs for sure, and that's not fixable. You'll have to send it for repairs, and hope they do something. Otherwise, you're out $300. Efs comes from the factory, it can't be remade. It's a special folder specific to your phone, with all of your identifying information such as imei and the code to read information from the sim card. I'm sorry man, it must suck to be in this position
Sent from my wonderful completely customized galaxy s3 running CyanogenMod 10.1.2