I think the Apple shop are a bunch of thieves. I would go straight to the owner of the shop with the information you just gave us. I realise they have to send the drive back to Apple to get paid but they could work with you. Maybe leave a deposit on it for a couple of weeks to give you a chance to recover. Your plan on a replacement board I give about a 20% chance of working. The only good thing about it is that you will have a drive to put on an external enclosure to do a Time Machine backup in the future.