Purge Night? Rob a Bank | The Purge (TV Series) 

Actually the banks move the money somewhere safe and secret, maybe even offshore. In the show, Ryan later finds out that they load the bundles from that specific bank onto a plane that's flying around at a high altitude for 12 hours until the Purge just ends. And since it RPGs or SAM launchers are off-limits, this basically prevents anyone from getting to the money by shooting the plane down. It's also nigh impossible to sneak on board due to the high security on the airfield. I also think that the plane normally takes off right before the sirens, so sneaking onto the airfield or the plane would be technically illegal and punishments for trivial offences such as trespassing are ridiculously harsh outside the Purge as Tommy's case would later show. I don't want to spoiler how they put up with this but they had to break laws off Purge to pull it off.

True but for what I believe imagine this was real the purge is a night of evil making deal with the devil