I'm not really a potential customer, but I'll jump in: $199 and $499 per month shocked me, and the range $29 to $499 completely confused me about your target customer. You should have an option marked "FREE" and in the same text as the paid options, and not just "free beta" but "free trial".
It seems like your target customer is someone who's not going to set up PhantomJS on their own, right? For 500 dollars I'll figure out how to set it up.
Another comment: the intro two paragraphs are probably more technical than they should be. The "what for" should be above the "headless browser" section; you might even put all of that stuff on a second "technical details" page to not scare people away. You're not selling "headless browsing" (anyone knows that they want that can probably set it up), you're selling "testing" and "screenshots" (and maybe other services too).
Late addition: saying "I'm not really a potential customer" isn't quite right. I'm putting together a hobby-project website with a lot of SVG images and have been thinking of looking into PhantomJS to generate pngs or gifs for browsers where svg isn't supported (preemptively in case this sounds stupid: that's way down the road, so I don't know if what I'm describing makes sense). I read your post and thought that I would be completely happy to spend a dollar or two a month (expected non-svg traffic is basically zero, but I'd like to support twitter cards) to support your project and generate the images on the fly using your service as a CGI, but 1) the pricing convinced me that the answer is "no" and 2) I'm no closer to knowing if what I want makes sense.
A few tutorials on how to do various tasks with your service would help a lot too (beyond the one-liners).
It seems like your target customer is someone who's not going to set up PhantomJS on their own, right? For 500 dollars I'll figure out how to set it up.
Another comment: the intro two paragraphs are probably more technical than they should be. The "what for" should be above the "headless browser" section; you might even put all of that stuff on a second "technical details" page to not scare people away. You're not selling "headless browsing" (anyone knows that they want that can probably set it up), you're selling "testing" and "screenshots" (and maybe other services too).