The reality here is that the cost to operate doesn't matter to Google. They can keep subsidizing Drive with revenue from Search Ads long after they have pushed Dropbox out of business, if they choose to do so.
This is why Dropbox (smartly) does not want to compete on price -- instead they want to compete on quality. There's no way to be cheaper than Google, Microsoft, Apple and Amazon in the long run, because they each have other businesses that are licenses to print money. If one or more of them decide to heavily subsidize their online storage product, they can outlast you.
However, it turns out that all of the money in the world can't magically make a great product. You still have to actually do the hard work.
This is why Dropbox (smartly) does not want to compete on price -- instead they want to compete on quality. There's no way to be cheaper than Google, Microsoft, Apple and Amazon in the long run, because they each have other businesses that are licenses to print money. If one or more of them decide to heavily subsidize their online storage product, they can outlast you.
However, it turns out that all of the money in the world can't magically make a great product. You still have to actually do the hard work.