When you think 'the money', you're probably counting sunk costs.

What do Thai Navy divers do? If there's no war on, they're probably training. What better training than a live rescue mission? I.e. the wages for those highly skilled Thai teams have probably been paid down already.

Similarly international forces benefit from co-operation because it's something they would want to do anyway: good will, training in co-operation, skills training.

As for volunteers their time is hardly a cost in the same way. But if you're a cave diving medic, the expected utility of using your time to save people in a cave is probably better than working and donating to a charity.

I’d bet 0. The money “saved” from not helping these kids would probably have saved exactly 0 other people.

Because for better or worse, that’s not how most money is redistributed.

I think you're viewing this wrong. This wasn't a one-time $2M spend on saving 12 people, this was cashing in on an insurance policy where citizens of Thailand pay premiums in forms of taxes.

Failing to save these kids is the case you want to think about - that would be sending the message to the public that if your kid gets lost in the mountains we're not going to save them. Sure this particular "insurance claim" (in this impromptu parlance) was an expensive one, but most of the others aren't, and the thing about insurance is that it is there particularly when the costs are catastrophic.