I think most SLAs for these types of services are mostly pointless anyway. If something important to your business goes down, are you really going to be worried about whether or not you have to pay the $19?
EDIT: If you have reasonable default tolerances or the ability to set tolerances on tasks, I'm pretty interested in trying it out - do you integrate or have plans to integrate with pagerduty, or do you simply fire off an email?
We don't replace something like monit to make sure your process continues to run, we are validation that one-off periodic things run... things that are easy to forget about but are important.