There's a really simple solution that people will hate: server goes offline at night.

I've seen this a few times, and it's pretty annoying as a user, but ultimately it's not that bad usually. If you are ordering something at 3am, the physical shipment still occurs during daylight hours. Many banking operations are not actually instantaneous, they settle in a batch job overnight.

And this doesn't have to be binary. Providing a read-only interface provides lots of value while having a reduced attack surface.