I'm pretty sure they're required to have cameras in the electronics department in order to have insurance. Further more, if they DO have insurance, they can't legally make you pay for it. If they don't, I would find out who theirs is with, and inform them that they may want to do a surprise visit to make sure the store is employing the security steps they say they are. The entire thing sounds like some sort of scam and that the manager could very well be pocketing the money for himself. I'd look around and see if you can get some legal advice somewhere.

You are not on the hook for that. Don't pay for it, your ex-boss is jut trying to scare you into doing so to get out of trouble.

Employers legally can NOT take more than 10% out of your pay for mistakes or errors. So if you've been fired and they failed to take up to 10% out of your final paycheck, you no longer have any legal obligation to pay for damages, and they could in fact get in trouble for pressuring you to pay. Particularly if- as it sounds- they have done so with some form of threat, implied or not.

Security cameras will tell the truth.