For example, maybe they have to shut down a busy highway for the prank call where several trucks with goods happen to drive on, or they have to evacuate nearby companies which have to shut down their work during the operation. The emergency services aren't really 'paying for it' but the economy for some people/organizations gets to a standstill for some at that moment. And that's only one example out of thousands. (part of) Those costs will always be for the tax-payer in one way or another, even if indirectly.
I hope you understand why it costs money when something economically-related gets to a halt
AND I hope you know what sort of things are economically related, which is basically anything that affects people & money. It can be as simple as one closed street or the temporary evacuation of a house.