How do I set up up notifications to be triggered when a safe is opened?

Hopefully somebody can help with a solution.
I run a post office where I need tight security. I basically need to know and see via remote link when my safe opens. I have no experience with cameras as such but I'm thinking that I need a sensor inside my safe to activate a camera when it's opened so I can view what's going on. Seeing live isn't as much an issue as long as it is recorded and I can access easily. Not though looking to spend a fortune on the system though.