hmm, something is weird there. It doesn't say how often the 600k hit their site, but presumably that's per month ("We have hundreds of thousands of hits per month"). Google Maps allows 25k map loads per day for free, which is already 750k for a 30 day month.
Even if you allow for overages that would cost money, it still doesn't add up. If you double that to 1.2 million per month, that's $12.50 a day, or $375 a month, which is still under the $499 a month Mapbox "Premium" Plan[2] (which only gets you 1 million loads per month).
And that's not even touching enterprise pricing, which presumably has a discount for volume (it's really dumb that gogole doesn't publish those enterprise prices though).