Wasnt sure about this. Do you need to pay to use an interupt?
Do you have to pay resources to use interupts?
Depends on the text of the interrupt and where the interrupt comes from. If it is an Event, you have to pay for the card. If the Interrupt effect is on a card that is in play, the card text will tell you if resources are needed to be paid (and possibly other costs as well).
Every card with a cost has an icon in the top left corner displaying it's cost. Some events have a cost of 0 - like Dark Precognition, with others costing much more (like A Price on Their Heads with a cost of 6). Unless something else lets you modify the cost, that printed cost is fixed.