I have seen SAAS's on microaquire listed with no customers. In fact I've seen them listed with no customers and no product! Who knows if those sell though.
Worth at least investigating.
Another option would be to pivot what you've built. So you have the stuff for slack and aws wired up. Forgotten ec2 instance sounds like something people would care about but based on your results maybe not as much as thought?
I wonder if there is something else in AWS you could alert via slack that people would care more about.
Expiring domains or ssl certs maybe? Though I'm not sure people care much about that either.
In any case, neat idea. I bet this experience will pay off big later in weird ways.