Assuming renders take 7-10 seconds at worst, that means (if I've got my math right!) that you need to do between (60m/(86400/7)=4861) and (60m/(86400/10)=6944) renders per second in order to keep up. (86400 = seconds in a day)
...Ahahahaha :)
Given that a single Chrome instance on my new-but-not-particularly-amazing i3 box can be sluggish at the best of times... I have no idea what sort of tolerances Xeon(?)-class hardware (possibly running Xen? :P) have to running multiple entire copies of Chromium... I initially wondered if you needed 1000 compute instance, then I realized maybe you only needed 400, now I honestly don't know at all.
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I'm also curious how using Headless Chrome and PhantomJS is working out. As in, genuinely interested. IIUC my understanding is that PhantomJS has pretty much wound down, while Headless Chrome is fractionally different enough from Chrome that it's possible to tell which one you're running on (https://news.ycombinator.com/item?id=14936025). I've been idly curious about "perfectly sandboxing" webpages so they honestly can't tell they're not in a "normal" PC/laptop/mobile environment, and my impression is that I'd have to start with a _very_ carefully configured copy of normal Chromium in order to do it.
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I must admit that I got curious at what 60m monthly renders looked like against the pricing structure... but couldn't really figure it out, it's not a simple enough exponential curve (and I can't math for nuts). Single-stepping through the pricing algorithm was very interesting though ($1522 for enterprise, huh cool).
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PS. The view-source link at the bottom is unfortunately broken; Chrome blocked opening such URLs recentlyish. Fixing it will likely require, ironically, a little server-side renderer :)
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EDIT: One last thing, note https://news.ycombinator.com/item?id=15882066 from this thread