What I really don't know is why I need a phantomjs web worker. I mean if I am that deep into testing, I have a CI which does this for me. No need to add another external service to the stack. I'm also worried that 1000 requests for $29 are a little much? I don't know about phantomjs, but zombiejs was installed in way under a minute (using npm). So while you are saving me a few minutes for installing phantom.js (doesn't look like rocket science to me), you are taking my time for integrating your API and you are charging me?
I think by refining your messages and thinking about what exactly it is you are selling you might have a decent service there.