I've used runscope.com and I love it. I don't know about their pricing so can't tell if it's suitable for someone in your situation but I'm sure there are tons

I've used runscope.com and I love it. I don't know about their pricing so can't tell if it's suitable for someone in your situation but I'm sure there are tons of similar services. You could also build your own with Lambda and hope AWS is reliable enough to keep Lambda running. (Who monitors the monitoring tools? :) )