Wowow! In this position my first step would be to determine if there's any legal basis for disputing the charge (an informal conversation with a lawyer or even just someone who's been through a similar experience is a fine start). Even when a billing change is disclosed in advance and the customer actually uses the bandwidth, massive spikes in metered pricing are a tricky area and have attracted the attention of regulators in the past--for instance telecoms have come under fire by charging sky-high overage fees for mobile data and not warning you until you've already racked up a few extra zeroes worth of charges on your next bill.

Also, immediately dispute the charge with your credit card company, as you want this on their radar. Their interests are aligned with yours to at least some degree (if Google's causing financial distress for one of their customers with thousands of dollars in unanticipated charges, how many others may get hit?).

Aside from that, if things played out as described: major dick move, Google! Is "do no evil" a bad joke these days? Seriously, though, Google is not a dumb company and my guess is that if the right person was made aware of this case (e.g., anyone who understands that the most important word in "customer relationship" is the second one), they would make it right.

I'm totally on the side of the author: when possible, it's worth a little extra elbow grease to build your business on top of free, self-hosted software instead of proprietary SaaS. Think of it as insurance against cases like this one.